For spellbook spells, the number next to the spellbook means you need that many spellbooks equipped to be able to research the spell. For example, 'Enchantment 8: Call of the Titans' means you need all 8 Enchantment spellbooks to research the spell Call of the Titans. Otherwise it'll never show up as a choice. If you don't customize spellbooks you'll never see spells above the 4th level! Also note that spells are not always immediately available to research: most spells require you to have gained a certain amount of lore (which I don't list here) before they show up as a research option.

By default, sovereigns use the following spellbooks:
Archlich: Chaos 4, Wrath 4
Commander: Chaos 2, Enchant 2, Summon 2, Wrath 2
Dwarven King: Enchant 2, Summon 2, Wrath 4
Guardian: Chaos 1, Enchant 3, Summon 4
Priestess: Chaos 3, Enchant 2, Summon 3
Tinkerer: Enchant 1, Summon 3, Wrath 4
Tyrant: Chaos 3, Enchant 1, Wrath 4
Wizard: Enchant 2, Summon 2, Wrath 4

The format for spell descriptions is:
Spell Name: [Spell Type, Mana Cost] Description

Starter spells are spells you have access to from the start of the game (no matter your sovereign or spellbook configuration). You don't need to research them; you can use them immediately.

Boost Shard, Bountiful Harvest, Enchanted Hammers, Enchanted Supplies, Lower Land, Raise Land, Spell of Ascendancy

Boost Shard: [Strategic, 50] Boost the output of a controlled shard by +1 Magic. Cooldown: 5
Bountiful Harvest: [Strategic, 12] Adds +3 food to the target city.
Enchanted Hammers: [Strategic, 30] Adds 3 material to your city. Can stack.
Enchanted Supplies: [Strategic, 20] Use an essence slot to gain +1 logistics.
Lower Land: [Strategic, 10] Lower a Mountain Range into passable terrain.
Raise Land: [Strategic, 10] Raise the land of a neutral tile.
Spell of Ascendancy: [Strategic, 50] Channel magic through a shard to create Ascension points towards godhood. Cooldown: 5

Universal spells are spells you have access to from the start of the game (no matter your sovereign or spellbook configuration). Unlike starter spells, you still need to research them, though.

Cloud Walk, Courage, Harvest Mountain, Harvest Forest, Heal, Restore Land, Summon Ship

Cloud Walk: [Strategic, 10] Teleports the caster, and their army, to a tile in friendly territory.
Courage: [Strategic, 5+1/turn] Instills legendary hope in the target, giving them a bonus of 5 (+1 per shard) to spell resistance and hit points.
Harvest Mountain: [Strategic, 30] Ruin target mountain to create metallic crafting ingredients at target tile location as well as metal.
Harvest Forest: [Strategic, 20] Ruin target forest to create wood related crafting ingredients at target tile location.
Heal: [Strategic, 6] Heals target unit by 10 (+3 per claimed shard).
Restore Land: [Strategic, 80] Turn target Grassland or Barren tiles into Fertile.
Summon Ship: [Strategic, 30] Summon a sea-faring vessel to help your forces explore the oceans riches.

Sovereigns start with certain spells (so they don't need to research them or have the necessary spellbook).

Decay: [Tactical, 6] For 6 turns the target enemies loses -3 HP per Turn, plus another 1HP per Shard. Cooldown: 6
Doom Gaze: [Tactical, 2] All enemy units are partially blinded for 3 turns, unless they resist. Cooldown: 4
Battle Cry: [Tactical, 30] All units get to act immediately. Cooldown: 3 (Also available with Enchantment 5)
Converge: [Tactical, 5] All friendly melee units converge on the target unit, who's [sp] defense is decreased by 75% for the next turn. Cooldown: 8
Ice Blast: [Tactical, 6] A[n] icey [sp] blast strikes for 8 (+3 per shard) in cold damage, and lowers Initative [sp] by 3. Cooldown: 2 (Also available with Wrath 2)
Obstruction: [Tactical, 2] Place an obstacle in a tile to prevent opponents from moving.
Awkward Movement: [Tactical, 2] Makes tiles treacherous causing units to be slowed way down while moving through them.
Obstruction: [Tactical, 2] Place an obstacle in a tile to prevent opponents from moving.
Soothing Melody: [Tactical, 25] All friendly units receive +2 hp per turn, while in battle.
Tame: [Tactical, 30] Take control of the targeted Beast, unless resisted. Cooldown: 6 (Also available with Chaos 4)
Destiny's Judgement: [Strategic, 1 DF] Bring down the wrath of the gods with a 75 arcane damage attack on target. Costs 1 Destiny's Favor.
Heavenly Ward: [Strategic, 0+1/turn+1 DF] Target unit will retreat to the nearest city when they lose a battle. Costs 1 Destiny's Favor and 1 Mana/turn upkeep.
Holy Vindication: [Tactical, 14] The skies part and holy light burns the wicked. All enemies take 2 Damage per allied unit.
Into the Light: [Tactical, 0] Does 3 damage to the target (+1 per Shard). If the enemy is killed, you receive that amount in Mana. Cooldown: 10
Refresh: [Tactical, 5] Unit goes immediately and refreshes all cooldowns. Cooldown: 10
Restore: [Tactical, 0] Restores target unit for 5 health plus 2 per shard. Costs no mana.
Summon Vorpal Blade: [Tactical, 4] Summon a Vorpal Blade into battle, crafted from mana and capable of Cleaving up to 3 adjacent enemies. Summoned level based on number of claimed Shards. Cooldown: 4
Summon Vorpal Longbow: [Tactical, 4] Summon a Vorpal Longbow into battle, crafted with mana and capable of hitting enemies from afar. Summoned level based on number of claimed Shards. Cooldown: 4
Summon Vorpal Spear: [Tactical, 4] Summon a Vorpal Spear into battle, crafted with mana and capable of Impaling a row of enemies. Summoned level based on number of claimed Shards. Cooldown: 4
Cauterize: [Tactical, 4] All friendly units heal 14 hit points (+3 per shard). Sorcerer King gains +6 Ascension Point. Cooldown: 5
Doomray: [Tactical, 5] Attack enemies in a 3x3 area with a blast of dark magic for 12 damage (+4 per Shard). Sorcerer King gains +1 Ascension Point. Cooldown: 3
Flame Dart: [Tactical, 5] A fiery dart strikes for 10 (+2 per shard) in fire damage. Cooldown: 2
Ice Blast: [Tactical, 6] A[n] icey [sp] blast strikes for 8 (+3 per shard) in cold damage, and lowers Initative [sp] by 3. Cooldown: 2 (Also available with Wrath 2)
Lightning Bolt: [Tactical, 8] An electrical blast strikes for 12 (+1 per shard) lightning damage. Shocks the target, disabling their special abilities for 2 turns. Cooldown: 2 (Also available with Wrath 2)

Chant of Vitality: (Default: Commander) [Strategic, 15] Your forces cannot rest while the enemy presses forward. This enchanted call will invigorate the target army - replenishing their moves. Cooldown: 1
Coercion : (Default: Tyrant) [Strategic, 25+1/turn] Target friendly city receives a 50% production boost.
Divine Wisdom: (Default Priestess) [Strategic, 25] Give a friendly unit a +1 boost to a random stat.
Earthly Familiar: (Default: Guardian) [Strategic, 25+1/turn] Summon an earthly creature onto the map.
Frostlanders: (Default: Dwarven King) Currently does nothing as of version 2.3.0.0. Seems to unlock 'Snowfall' spell which doesn't exist- should probably be 'Snowstorm'. [Strategic, 26] Turn tile into Arctic terrain.
Hypnotism: (Default: Wizard) [Tactical, 30] Cast on an enemy unit in battle, for a chance that they'll join your side. Cooldown: 6
The Undying: (Default: Archlich) [Strategic, 20+2/turn] Target unit will retreat to the nearest city when they lose a battle. Costs 2 Mana/turn upkeep.
Transmutation: (Default: Tinkerer) [Strategic, 25] Summon a random item.

Note: I didn't check if they actually unlock anything except for the Priestess.

'Lands of Magic' (Unlocks 'Reanimation'): [Strategic, 6] Completely heal and replenish the moves of any Army stationed in Blue Fissure terrain. Cooldown: 1
'From the Depths': [Strategic, 4] Teleport your units onto a Blue Fissue [sp] tile.
'Cold Hands' (Unlocks 'Death Grip'): [Strategic, 2] Target enemy army is -2 Initiative (-1 per shard) and immobilized for 2 turns (including the current turn). Must be cast in Blue Fissure. Cooldown: 4
'The Reaping': [Strategic, 15] A powerful offensive spell that halves the HP of any enemy army passing through Blue Fissure terrain. Cooldown: 1
'Battle Tactics' (Unlocks 'Enrage' and 'Indiscriminate Wrath'): Enrage: [Tactical, 0] All friendly units get +1 attack bonus every time they're hit in battle. No mana cost. Indiscriminate Wrath: [Tactical, 0] All units take 1 point arcane damage. No mana cost.
'Call to Arms' (Unlocks 'Warrior's Call' and 'Defender's Call') Warriors Call: [Tactical, 0] All friendly units get a +2 attack bonus. No mana cost. Defenders Call: [Tactical, 0] All friendly units get a +2 defensive bonus. No mana cost.
'Frozen Tracks': [Strategic, 0] All enemy units are frozen on the strategic map for 10 turns. Cooldown: 99
'Stunted Growth': [Strategic, 0] Unlocked a Storm Call where spawned Sorcerer King units get a -50% level penalty and can not gain experience for 25 turns. Cooldown: 99999
'Earthbreaker': [Strategic, 0] A Storm Call that rips open the earth. Target enemy of any level is swallowed into a chasm. Cooldown: 50
'Stoneguard': [Strategic, 0] Raise a barrier of mountains around the target Shard. Cooldown: 50
'Freezing of the World': [Strategic, 0] Freeze a large section of the world. Cooldown: 20
'Revive Land': [Strategic, 64] Turn target shadow tile into a fertile tile.
'Geomancy' (Unlocks 'Restore Land'): [Strategic, 80] Turn target Grassland or Barren tiles into Fertile. (Also available normally after 400 Lore)
'Shard Healer' (Unlocks spell that allows player to heal shards): Heal Shard: [Strategic, 50] Use 50 mana to heal an elemental shard by 10 HP.
'Fertility': Fertilily[sp]: [Strategic, 100] Places a Wild Grain tile on the map.
'Volcanic Vengeance' (Unlocks 'Volcano'): [Strategic,300] Raises a volcano in the midst of your enemies. The volcano destroys units, resources, and even cities on the land it targets. (Also available with Wrath 8)
'Heroic Precision': [Tactical, 0] Target unit never misses for duration of battle.
'Destiny's Sentinel': Conjure Destiny's Sentinel: [Strategic, 0+1 DF] Use your divine favor to summon a holy Sentinel to fight alongside your troops.
'Holy Wrath' Currently does nothing as of version 2.3.0.0. [Strategic, 0+1 DF] Target tiles are filled with righteous wrath doing damage to all enemies who dare pass through.
'Malevolence' (Unlocks 'Drain Shard'): [Strategic, 0] Destroy any shard in your territory, draining 300 mana from it instantly. Increases the Sorcerer King's Ascension Points by +50.
'Scorched Earth': [Strategic, 64] Bring down your wrath onto the target unit. Permanently damages tile it is in. Does up to 50 arcane damage.
'Replenish Armies': [Strategic, 100] Completes training of any units being trained in your cities. Cooldown: 5
'Wrath of God' (Unlocks 'Falling Star'): [Strategic, 100] Does 18 fire damage (+3 per shard) to all armies within 1 tile of the impact point. Cooldown: 1 (Also available with Wrath 8)
'Demonic Reinforcements' (Unlocks 'Armageddon'): [Strategic, 40] Opens a portal to release demonic allies into your world. Increases the Sorcerer King's Ascension Points by +5. Cooldown: 1 (Also available with Chaos 8)
'Geomancy' (Unlocks 'Restore Land'): [Strategic, 80] Turn target Grassland or Barren tiles into Fertile. (Also available normally after 400 Lore)

Chaos 1: Beguile, Chaos, Curse, Death Lash, Slow, Storm
Chaos 2: Drain Life, Equal Odds, Freeze, Giant Form, Shadowbolt
Chaos 3: Black Mirror, Enfeeble, Fracture, Sacrifice
Chaos 4: Aura of Madness, Heroic End, Silence, Tame
Chaos 5: Confusion, Mass Curse, Touch of Entropy
Chaos 6: Imprision, Pandemonium, Tornado
Chaos 7: Diamondskin, Mass Slow
Chaos 8: Armageddon

Enchantment 1: Eyes of the Eagle, Focus, Hold the Line, Marksman's Boon, Nature's Bounty, Tireless March, Tutelage
Enchantment 2: Aether Trap, Aura of Grace, Aura of Vitality, Haste, Inspiration, Warrior's Might
Enchantment 3: Aura of Might, Crusade, Starlit Crown, Warrior's Aura, Withstand
Enchantment 4: Champion's Call, Destiny's Gift, Eternal Supply, Wellspring
Enchantment 5: Battle Cry, Divine Protection, Divine Speed
Enchantment 6: Arcane Veil, Gift of Iron, Starlit Armor
Enchantment 7: Aura of Entropy, Mana Shield
Enchantment 8: Call of the Titans, Death Ward

Summoning 1: Guardian Wind, Place Road, Summoner's Aura, Summon Bear, Summon Imp, Raise Skeleton
Summoning 2: Conjure Mud, Summon Shadow Warg, Summon Wisp
Summoning 3: Obscuring Fog, Summon Hergon, Summon Ice Elemental
Summoning 4: Raise Skeletal Horde, Summoner's Boon, Summon Iron Golem
Summoning 5: Summon Air Elemental, Summon Fire Elemental, Summon Arachnos
Summoning 6: Conjure Ice Elemental, Summon Morian, the Swamp Collossus, Summon Assassin Demon
Summoning 7: Conjure Fire Elemental, Summon Torax, the Rock Collossus
Summoning 8: Conjure Air Elemental, Summon Delin, the Colossus of Ash

Wrath 1: Blinding Flash, Contagion, Mantle of Fire, Pillar of Flame, Shrink, Wrath of Fire
Wrath 2: Fireball, Ice Blast, Inferno, Lightning Bolt, Sunder, Winter's Wrath
Wrath 3: Candlecloak, Soulburn, Spell Leech, Wrath of Thunder
Wrath 4: Blood Sigil, Flame Wave, Wall of Fire
Wrath 5: Arcane Wrath, Blizzard, Graveseal
Wrath 6: Mana Blast, Mass Berserk, Overkill
Wrath 7: Consume, Kill
Wrath 8: Falling Star, Volcano

Beguile: [Strategic, 2] Victim has a 50% chance to swing at a random unit in melee instead of his target.
Chaos: [Strategic, 2] Does a random effect to target enemy unit unless they resist.
Curse: [Strategic, 5] Target has no Defense for 3 turns. Cooldown: 2
Death Lash: [Strategic, 10] Target unit gets +8 to Attack and Initiative, but the unit loses 2 HP per turn. Cooldown: 2
Slow: [Strategic, 4] Target enemy unit suffers -10 to Initiative, unless resisted. Cooldown: 1
Storm: [Strategic, 10] Lightning strikes a random enemy group for 20 Lightning damage (+4 per shard). Cooldown: 3

Drain Life: [Strategic, 12] Drain 12 Hit Points (+2 per shard) from the target enemy and use it to heal the current friendly unit. Value is cut in half if resisted.
Equal Odds: [Strategic, 20] All units, both enemy and ally alike, lose their defense for the course of the battle. Cooldown: 6
Freeze: [Strategic, 4] Target enemy army is -2 Initiative (-1 per shard) and immobilized for 4 turns (including the current turn). Cooldown: 5
Giant Form: [Strategic, 12] 50% bonus to target's Attack but lowers Dodge by 10.
Shadowbolt: [Strategic, 6] A bolt of night strikes the victim doing 5 damage and reducing their Spell Resistance by -10 (-2 per shard). Cooldown: 1

Black Mirror: [Strategic, 12] 75% of melee damage done to the target is reflected to the attacker for 5 turns.
Enfeeble: [Strategic, 18] Reduces the attack of the enemy army by -2 (-1 per Shard), half that value if resisted. Effect lasts for 5 turns.
Fracture: [Strategic, 20] Target unit loses 40% of his Hit Points and Defenses - 10% if resisted. Cooldown: 2
Sacrifice: [Strategic, 0] Target city sacrifices half its citizens to produce 1 mana per sacrifice.

Aura of Madness: [Strategic, 20] Enemy units fighting in your ZOC suffer a penalty of -3 Defense and -20 accuracy, but get +2 Attack.
Heroic End: [Strategic, 10] Target unit gets 3X its current attack and full HP but dies at the end of the battle.
Silence: [Strategic, 8] Target unit cannot use abilities for the rest of the battle (unless they resist). Cooldown: 1
Tame: [Strategic, 30] Take control of the targeted Beast, unless resisted. Cooldown: 6

Confusion: [Strategic, 26] All enemies have a 50% chance to swing at a random unit in melee instead of their target, unless they resist. Cooldown: 1
Mass Curse: [Strategic, 28] Removes all enemies Defense for 5 turns unless they resist. Cooldown: 2
Touch of Entropy: [Strategic, 35] Does 24 damage (+6 per shard) to unit. If that unit is killed a Lurk is summoned in its place. Cooldown: 1

Imprision [sp]: [Strategic, 26] Target enemy is immobilized for 5 rounds and takes 5 damage per round, unless they resist. Cooldown: 3
Pandemonium: [Strategic, 15] Does a random effect to all enemy units unless they resist. Cooldown: 2
Tornado: [Strategic, 30] Units in the target army are randomly scattered, immobilized for a turn and lose 50% of their health. Cooldown: 1

Diamondskin: [Strategic, 30] Unit is immune to physical damage for 3 turns.
Mass Slow: [Strategic, 25] Target enemies suffer -4 to Initiative (-1 more per shard). Cooldown: 2

Armageddon: [Strategic, 40] Opens a portal to release demonic allies into your world. Increases the Sorcerer King's Ascension Points by +5. Cooldown: 1

Eyes of the Eagle: [Strategic, 25] Permanently reveals a 6x6 area of the map. Enemy units are only visible for 1 turn. Cooldown: 1
Focus: [Strategic, 8] The target unit gets +25% Attack for the rest of the battle and all abilitiy cooldowns are immediately replenished. Cooldown: 4
Hold the Line: [Strategic, 10] All allied units fighting in friendly territory start defending and get +40 Dodge for 2 turns.
Marksman's Boon: [Strategic, 5] Target unit gets +100 Accuracy for the rest of the battle.
Nature's Bounty: [Strategic, 20] +1 Food per level in the enchanted city. Can stack.
Tireless March: [Strategic, 20+1/turn] Increases the movement of the target's army by 1.
Tutelage: [Strategic, 15+1/turn] Target unit gains experience at a 25% faster rate.

Aether Trap: [Strategic, 18] A tile in tactical combat damages any enemy unit that passes through it by 2 (+2 per Shard). Cooldown: 1
Aura of Grace: [Strategic, 40] Boosts the Initiative of units trained in this city by +1 per essence.
Aura of Vitality: [Strategic, 20] A City Enchantment that boosts the HP of units trained in this city by +3 (+1 per essence).
Haste: [Strategic, 6] Target unit gets +15 to Initative. Cooldown: 1
Inspiration: [Strategic, 25] Inspire Hope in the people of your city. Reduces Thralls in the city by 5.
Warrior's Might: [Strategic, 5] Target unit gets +2 attack per attack for the duration of battle.

Aura of Might: [Strategic, 25] All units trained in this city are +1 Defense per Essence.
Crusade: [Strategic, 130] All trained units gain 1 level.
Starlit Crown: [Strategic, 20] Creates a helm that doesn't provide defense but grants Spell Resistance.
Warrior's Aura: [Strategic, 30] +3 Level Bonus to units trained in this city.
Withstand: [Strategic, 15] Unit is immune to Cold, Fire and Lightning damage for the remainder of battle. This also puts the unit into a defending stance. Cooldown: 5

Champion's Call: [Strategic, 30] All allied Champions get +1 attack, initiative, defense, dodge and accuracy per shard. Lasts for the rest of combat.
Destiny's Gift: [Strategic, 250] Target Champion gets a permanent +1 boost to Hit Points, Attack Strength, and Initiative per Shard.
Eternal Supply: [Strategic, 80] Target city supplies +1 logisitcs per essence.
Wellspring: [Strategic, 30] All members of the targeted army heal 24 hit points (+4 per shard).

Battle Cry: [Strategic, 30] All units get to act immediately. Cooldown: 3
Divine Protection: [Strategic, 50] Target is invincible for 3 turns. Cooldown: 2
Divine Speed: [Strategic, 40] Target unit gets to move immediately and gets +20 initiative for the duration of the battle. Cooldown: 6

Arcane Veil: [Strategic, 20] This unit resists all spells for the remainder of battle. Cooldown: 2
Gift of Iron: [Strategic, 20] All allied units have their Defense raised by 5 (+2 per shard).
Starlit Armor: [Strategic, 30] Creates armor that doesn't provide much defense but grants massive Spell Resistance.

Aura of Entropy: [Strategic, 100] When fighting in your territory, wild magics tear at the enemy army at the beginning of every combat, reducing their hit points by 25%.
Mana Shield: [Strategic, 5] Damage taken by the target is ignored. Instead mana is lost from the mana pool. Cooldown: 1

Call of the Titans: [Strategic, 50] All unstationed units will be teleported to the selected tile. Cooldown: 5
Death Ward: [Strategic, 50+1/turn] If this unit is killed in battle they are resurrected with all their hit points restored (but removes the enchantment).

Guardian Wind: [Strategic, 10] Summon a Wind arround all allied units, giving them +50 to Dodge vs ranged attacks.
Place Road: [Strategic, 5] Player can build a road on any tile via the spell book.
Raise Skeleton: [Strategic, 1] Raise a Skeleton from the ruins of Elemental. Though weak, a skeleton costs only 1 mana to summon.
Summoner's Aura: [Strategic, 20+1/turn] Reduce summon costs in this city by 25%.
Summon Bear: [Strategic, 5] Summon a slow moving but deadly Bear, who will continue to Maul his target until she misses. Cooldown: 2
Summon Imp: [Strategic, 5] Summon a weak but wily Imp, who refreshes his moves whenever he's hit. Cooldown: 1

Conjure Mud: [Strategic, 10+4/turn] Changes the terrain within a 1 tile radius to mud. Units can only move 1 tile per turn through mud. Cooldown: 1
Summon Shadow Warg: [Strategic, 10] Summon Shadow Warg into battle, striking fear in all adjacent enemy units. Cooldown: 3
Summon Wisp: [Strategic, 10] Summons a level 2 (+1 per shard) Wisp and heal all allies within 1 tile for 8 hit points. Cooldown: 1

Obscuring Fog: [Strategic, 12] Summons a fog that blurs your units and improves their Dodge by 20 (+1 per shard).
Summon Hergon: [Strategic, 8] Summons a mighty horned Hergon to bash your enemies around the battlefield. Cooldown: 1
Summon Ice Elemental: [Strategic, 15] Summons a fragile but frigid Ice Elemental, freezing all enemies for a turn. Cooldown: 5

Raise Skeletal Horde: [Strategic, 15] Raise a skeletal horde from the ruins of Elemental. Cooldown: 2
Summoner's Boon: [Strategic, 5] Target summoned unit get a 50% boost to attack, 50% boost to defense, and gets to move immediately. Cooldown: 3
Summon Iron Golem: [Strategic, 10] Summon an Iron Golem into battle, boosting the defense of all adjacent friendly units. Cooldown: 1

Summon Air Elemental: [Strategic, 30] Summon an Air Elemental into battle. Shocks all adjacent enemies, disabling their special abilities for 2 rounds. Cooldown: 3
Summon Fire Elemental: [Strategic, 25] Summons a Fire Elemental onto the battlefield, engulfing the tiles around him. Cooldown: 3
Summon Arachnos: [Strategic, 18] Summon the spider spirit Aracnos, an ancient beast that can entangle enemies in its posionous web. Cooldown: 2

Conjure Ice Elemental: [Strategic, 40+1/turn] Conjure a Ice Elemental onto the strategic map. Requires 1 Mana per turn.
Summon Morian, the Swamp Collossus: [Strategic, 40] Summon Morian, the Swamp Collossus of the past age, into battle. All enemies are poisoned. Cooldown: 10
Summon Assassin Demon: [Strategic, 14] Summon an Assassin Demon into battle, who lowers the Initiative of adjacent enemies and gets to move immediately. Cooldown: 2

Conjure Fire Elemental: [Strategic, 50+1/turn] Conjure a Fire Elemental onto the strategic map. Requires 1 Mana per turn. Cooldown: 5
Summon Torax, the Rock Collossus: [Strategic, 50] Summon Torax, the Rock Collossus of the past age, into battle. All allies get a 50% boost to physical defense. Cooldown: 10

Conjure Air Elemental: [Strategic, 60+1/turn] Conjure an Air Elemental onto the strategic map. Requires 1 Mana per turn.
Summon Delin, the Colossus of Ash: [Strategic, 70] Summon Delin, the Ash Colossus of the past age, into battle, igniting all tiles around him. Cooldown: 20

Blinding Flash: [Strategic, 8] Target enemies are stricken blind, resulting in a 50% penalty to Accuracy (10% if resisted). Cooldown: 2
Contagion: [Strategic, 10] All enemy units take 2 poison damage (+1 per shard) per turn for 10 turns, unless they resist. Cooldown: 1
Mantle of Fire: [Strategic, 10] Wreaths the target in flames, doing 6 fire damage to anyone who attacks him. Also gets +1 fire damage to melee attacks per level. Cooldown: 1
Pillar of Flame: [Strategic, 10] Target enemy army takes 6 fire damage (+1 per shard).
Shrink: Target enemy's Attack is halved, but gains +30% to Dodge. Cooldown: 1
Wrath of Fire: [Strategic, 10] City Enchantment that adds +1 Fire Attack to all allied units when fighting in the player's Zone of Control.

Fireball: [Strategic, 15] Fireball does 5 fire damage (+3 per shard) to enemy units within a 1 tile radius - half that if resisted. Cooldown: 2
Ice Blast: [Strategic, 6] A icey blast strikes for 8 (+3 per shard) in cold damage, and lowers Initative by 3. Cooldown: 2
Inferno: [Strategic, 25] Target tile is on fire for 10 turns, walking through the tile causes 5 damage to each member of the group.
Lightning Bolt: [Strategic, 8] An electrical blast strikes for 12 (+1 per shard) lightning damage. Shocks the target, disabling their special abilities for 2 turns. Cooldown: 2
Sunder: [Strategic, 20] Target Elemental takes 5 damage per shard - half that if resisted.
Winter's Wrath: [Strategic, 20] City Enchantment that adds +1 Cold Attack to allies and -2 Initative to enemies when fighting in your territory.

Candlecloak: [Strategic, 18] Wreathes all your units in flames, doing 3 fire damage (+1 per shard) to anyone who attacks them.
Soulburn: [Strategic, 10] Sacrifice a trained unit to do 1/2 their Max HP as a fire attack on all enemy units. Adds 3 to the Sorcerer King's Ascension Points. Cooldown: 2
Spell Leech: [Strategic, 0] Disrupts a spell an enemy unit is casting unless they resist. If successful this spell also grants the caster 40 mana.
Wrath of Thunder: [Strategic, 10] City Enchantment that adds +2 Lightning Attack to all allied units when fighting in the player's Zone of Control.

Blood Sigil: [Strategic, 20] All friendly units go Berserk while all enemy units are withered.
Flame Wave: [Strategic, 30] Brings forth a wave of flame that causes 8 (+2 per shard) fire damage to all enemy units - half that if they resist. Cooldown: 2
Wall of Fire: [Strategic, 20] Units that attack this city take 10 (+3 per shard) in fire damage at the start of combat.

Arcane Wrath: [Strategic, 10] Does 30 damage to a random enemy.
Blizzard: [Strategic, 80] Enemy units in a 2 tile radius take 8 cold damage (+2 per shard), get penalized -1 Initative [sp], and -10 Dodge. Cooldown: 2
Graveseal: [Strategic, 20] Target unit suffers critical hits from all attacks. Cooldown: 2

Mana Blast: [Strategic, variable] A blast of arcane energy that does damage equal to one tenth the players stored mana (consuming that mana in the process). If the victim resists that damage is halved. Cooldown: 3
Mass Berserk: [Strategic, 10] All allied units gain +2 Attack (+1 per shard) but take 1 damage per turn.
Overkill: [Strategic, 30] Do 4 damage to every enemy unit for every unit in the caster's army (half that if resisted). Cooldown: 4

Consume: [Strategic, 0] Destroy a shard to gain 300 mana. Sorcerer King gets a +35 point boost towards Ascension.
Kill: [Strategic, 60] Target unit dies, unless they resist.

Falling Star: [Strategic, 100] Does 18 fire damage (+3 per shard) to all armies within 1 tile of the impact point. Cooldown: 1
Volcano: [Strategic, 300] Raises a volcano in the midst of your enemies. The volcano destroys units, resources, and even cities on the land it targets.

The Shadow spellbook seems to be for the Sorcerer King but you can access it if you manually edit the custom sovereign file.

Blight (Starter Spell)

Blight: [Strategic, 0] All players lose 50% of their population. Cooldown: 10

There are spells that are in the game files but aren't actually available in-game (without doing some editing, and may not work properly even if you do add them back in). I'm only mentioning spells that are tagged for specific spellbooks but there are more.

Chaos 1: Daze: [Tactical, 8] Target enemy loses next 2 turns. If resisted, unit only loses 1 turn.
Chaos 2: Blink: [Strategic, 8] Teleport the current unit to any tile on the battlefield.
Chaos 3: Call Lightning: [Strategic, 18] Summon a storm into the battlefield, dealing 6 Lightning Damage (+2 per shard) on all enemies. Value is cut in half if resisted.
Chaos 4: Earthquake: [Strategic, 0] Destroys random city improvements, resets the production queue and halves the population of the targeted city. Cooldown: 1
Enchantment 1: Stoneskin: [Strategic, 2] Target unit's Defense is raised by 7 (+1 per shard). Cooldown: 1
Summoning 1: Recall: [Strategic, 0] Teleports the caster, and their army, to your capital.
Summoning 3: Conjure Outpost: [Strategic, 200] Creates an Outpost on the map which extends your Zone of Control. Cooldown: 10
Summoning 3: Seal of Hope: [Strategic, 100] Target city gains 40 population.
Wrath 2: Barbs: [Strategic, 5] Does 16 damage to the target and the current unit.
Wrath 2: Grip of Winter: [Strategic, 12] Target stronghold can not train units or spread Shadowland for 5 turns. Cooldown: 25
Wrath 3: Incinerate Stronghold: [Strategic, 20] Units stationed in the target stronghold take 5 fire damage apeice [sp].
Wrath 4: Firestorm: [Strategic, 40] All units in target army take 8 fire damage (+2 per shard). Firestorm leaves a raging fire in the affected filre for 10 turns.
Wrath 5: Thunderstrike: [Strategic, 15] Teleport to a location and do 10 lightning damage (+2 per shard) to all enemies within 1 radius.
Shadow 1: Frozen Bones: [Strategic, 0] Target city is crippled with an unnatural coldness slowing stationed units and reducing their Initiative by 3.

Compassion: Summon Shadow Warg: [Tactical, 10] Summon Shadow Warg into battle, striking fear in all adjacent enemy units. Cooldown: 3 (Also available with Summoning 2)
Cowardice, Fame: Escape: [Tactical, 10] All units flee from the battlefield.
Cruelty: Domination: [Tactical, 10] Take control of enemy unit unless they resist. Sorcerer King gains +5 Ascension Points. Cooldown: 6

After you unlock the Enchanting tab of Crafting, you can use enchantments based on what spellbooks you've chosen. All enchantments seem to cost 5 Mana.

Chaos 1: When unit dies, all friendly units become enraged
Chaos 2: +10% Damage Reflect
Chaos 3: +10 Accuracy
Chaos 4: Unit explodes when killed, damaging anyone nearby
Chaos 5: +50% Maul Chance
Chaos 6: +5 HP From Kills
Chaos 7: +5 Mana From Kills
Chaos 8: Unit casts Flamewave on death

Enchantment 1: +4 Defense
Enchantment 2: +15 HP
Enchantment 3: +10 Fire Resist
Enchantment 4: +10 Cold Resist
Enchantment 5: +10 Poison Resist
Enchantment 6: Whenever this unit dodges, it gets a counterattack
Enchantment 7: +10 Dodge
Enchantment 8: +1 Cannot Die

Summoning 1: Raise Skeleton (Unit can summon in a skeleton into battle)
Summoning 2: Call Wolf (Unit can call in a wolf into battle)
Summoning 3: Nature's Call (Unit can call in a nature ally into battle)
Summoning 4: Escape (Cause all units to flee from the battlefield)
Summoning 5: -20% Rush costs in stationed city
Summoning 6: +2 Bonus Summoned Levels (When this unit is in an army, all summoned units are brought in with a level boost of +2)
Summoning 7: +5 Health Regeneration (+5 HP per turn on the Strategic Map)
Summoning 8: +3 Tactical Health Regeneration (+3 HP per action in Tactical Combat)

Wrath 1: +10 Backswing
Wrath 2: +3 Physical Attack Bonus
Wrath 3: +3 Fire Attack
Wrath 4: +3 Cold Attack
Wrath 5: +5 Critical Damage
Wrath 6: +2 Poison Damage
Wrath 7: +5 Critical Chance
Wrath 8: Coalstones hits all enemies when this unit dies

'Master Enchanter' (Unlock several high-level enchantments from the Wrath, Summoning, Enchantment, and Chaos spellbooks): This lets you access Chaos 7, Chaos 8, Enchantment 7, Enchantment 8, Summoning 8, and Wrath 8 enchantments.