Traits List:

AA Support - Provides support fire against air to ground attacks. Will shoot at any fighters and bombers attacking friendly ground units within its firing range

Aggressive Counterattack - +3 attack when defending

Aiming Assistance - +10% accuracy to all adjacent friendly units

All-Terrain Entrenchment - Entrenches in any terrain with Maximum speed

Alpine Troops - Gets +5 attack and +5 defense in hills and mountains and also ignores enemy High ground bonuses and entrenchment in such terrain (Unit Trait)

Ambusher - Always Triggers an Ambush when attacked

Artillery Support - Provides support fire to adjacent friendly units attacked by enemy unarmoured units (with "Soft" target type).

Anti-tank support: the unit provides support fire against hard targets (basically the same ability as tank destroyers)

Avenger - Gets attack bonus for each point of lost strength

Bridging Unit - Acts as a bridge when positioned on a river (Unit Trait)

Bunker Killer - +5 attack against structures (Unit Trait)

Butcher - +5 attack against infantry units

Camouflage - Can only be detected by recons or adjacent ground units

Cheap Replacements - Replacements in battle cost as on deployment phase

City Fighter - Combat Bonus in city terrain

Close Combat - Has access to enemy unit's close defense rating when fighting in close terrain (Unit Trait only)

Combat Luck - Combat Results can never be worse than predicted

Counter Battery Fire - Will fire at any attacking artillery units within its firing range

Crippling Blow - +5 Attack against full strength units

Distraction - Enemy units next to this unit do not provide support fire

Double Attack - Unit gets 2 attack actions per turn

Double Mass Attack - When participating in Mass Attack, contributes double effect.

Double Move - Unit gets 2 move actions per turn, without increasing the number of movement points

Double Support - Provides support fire twice for each enemy attack

Entrenchment Killer X - Destroys X points of entrenchment with every attack

Entrenchment Support - All adjacent friendly units entrench at 2x speed (Unit Trait Only)

Envelopment - Prevents enemy units from retreating, so they surrender instead

Evasive - -10% accuracy to enemies shooting at this unit

Expert Recon - Provides 3x accuracy bonus on adjacent enemy units

Expert Support - +20% accuracy when providing support fire

Exterminator - +5 attack against units below 50% strength

Famous - Generates 20 prestige per turn

Fast Deployment - can unmount from organic transport and fire after movement

Fast Entrenchment - Gets 2x entrenchement speed

Fast Learner - 2x Faster experience growth

Fast Rebase - Aircraft does not spend Move Action on rebase

Fast Retreat - +2 movement points when unit's strength is 33% from maximum

Fearsome Reputation - All Adjacent enemy units get +3 suppression at the beginning of their turn

Ferocious Defense - Entrenchment of this unit cannot be ignored

Field Repairs - Restores one point of strength every turn the unit did not attack. Applies to Vehicles

Fierce Fighter - +1 attack for each adjacent enemy unit

Fighter Suppport - Provides support fire against enemy fighters attacking friendly bombers. Will also intercept enemy bombers attacking friendly ground units in adjacent hexes (Unit Trait only)

First Aid - Restores one point of strength every turn the unit did not attack. Applies to Infantry.

First Strike - Unit always attacks first

Flag Killer - +5 Attack when attacking enemy flags

Glider - Can Land and disembark the unit it carries on any land hex, not just airfields. Exceptions are hexes which are impassable for embarked unit.

Hit and Run - When attacking, enemy units with the lower initiative do not shoot back

Ignores Entrenchment - Ignores enemy entrenchment level

Ignores ZOC - Ignores zone of control projected by enemy units when moving

Learns from Mistakes - 3x experience for suffered casualties

Lethal Attack - Half of suppression caused by this unit is converted to kills

Liberator - 2x prestige for all flags captured by this unit

Lightning Attack - Immune to all types of support fire

Low Profile - Enemy units get -20% accuracy when shooting at this unit

No Entrenchment - Unit does not entrench

No Surrender - Unit never surrenders

No Retaliation: enemy units will not return fire if attacked by that unit

Overrun - Can destroy (Overrun) weakened enemy units without spending move or attack actions. The way it works is, after and overrun attack, move and attack actions of the unit will be replenished

Overwhelming Attack - Any Damage to enemy units is enough to force them to retreating

Phased Movement - Can move in steps within its movement point limit (like recon)

Provocator - Adjacent enemies attacking other friendly units will attack this unit instead

Prudent - Gets defense bonus for each point of lost strength

Rapid Fire X - Makes X more shots than normal and consequently deals X damage to the target.
This trait does not affect ammo spending, the unit still consumes 1 ammo per attack

Readiness - Strikes first when defending

Reduced Slots - Unit slot cost is reduced by 50%.

River Fighters: Ignores Battle Penalties through River Fields

Scavenger - Captures 2x equipment from surrendering enemies.

Shock Tactics - When attacking, pins enemy unit in place by destroying all its movement points

Sixth Sense - Immune to Ambushes

Superior Manuever - Gets +1 initiative for each point of movement speed advantage over the enemy

Tank Killer - +5 attack against tanks

Tenacious Defender - +1 defense for each adjacent enemy unit

Thorough Preparation - Initiative bonus +5… +1 on the first five turns of every mission

Unyielding - Unit cannot be suppressed by enemy fire

Vigiliant - Prevents enemies from using unit's Close Defense rating

Vulnerable Target - Enemy units always shoot at this unit with 100% accuracy

Zero Slots - Unit slot cost is reduced to zero

Bundled strength: +5 strength points for the unit (tanks can have a maximum of 20, infantry 25 points/overstrength)

Ignore Mass Attack: Immunity to mass attack

Last Stand: Ignores all penalties from encirclements

Alpine*: Gets +5 Attack and +5 Defence in hills and mountains, and also ignores enemy High Ground bonuses and Entrenchment in such terrain

*Alpine is usually found on mountain troops but a hero was added in Frontlines Cyracenia DLC that has this trait

In no particular order:

Adolf Galland:
Fighter Class
Tactical Bomber Class
+2 to Initiative
+2 to Air Attack
Legendary (Generates 50 Prestige per turn)
Aiming Assistance (+10% accuracy to all adjacent units) *Includes ground units
Leadership (+1 Initiative to all adjacent friendly units)

Albert Kerscher:
Tank Class
Anti-Tank Class
+3 to Initiative
Famous (Generates 20 Prestige per turn)
Tank Killer (+5 Attack against Tanks)
Aggressive Counterattack (+3 Attack when defending)

Oleh Dir:
Infantry Class
+2 to Initiative
+2 to Speed
Famous (Generates 20 Prestige per turn)
Precision Weapon (+20% base Accuracy)

Hans-Ulrich Rudel:
Legendary
Double Attack/(Something else I don't remember)
Lightning Attack/(Something else I don't remember)
Tank Killer/Ignores entrenchment

Helmut Wirnsberger:
Infantry Class
+3 Initiative
+1 Speed
Low Profile
Ignores ZOC

Karla Wuhrer:
Anti-Tank Class
Anti-Aircraft Class
Rapid Fire 2x
Fast Learner

Gero Von Manstein:
Infantry Class
Zero Slots
Vigilant

Karl Ullmann:
Anti-Tank Class
Anti-Aircraft Class
Rapid Fire 2x
Learns from Mistakes

Helga Grese (1945 Historical):
Anti-Tank Class
Anti-Aircraft Class
Skilled Support
Aiming Assistance
Crippling Blow

Otto Carius (1945 Ahistorical):
Tank Class
Anti-Tank Class
+2 Speed
Crippling Blow

Beate Uhse (1945 Ahistorical):
Fighter Class
Tactical Bomber Class
+1 to Initiative
Aiming Assistance
Zero Slots

Capitana Vigano (1946):
Tank Class
Anti-Tank Class
+1 Speed
Double Attack
Thorough Preparation
Legendary

Frontlines - Bulge:

William Hunt:
Aggressive Counterattack
Fast Entrenchment
First Aid

Frank Murphy:
Tank Killer
No Retaliation

Johnathan Taylor:
Fast Learner
Hit and Run

Robert Knight:
Rapid Fire 1.5x
Cheap Replacements

Frontlines - Cyreancia
British Side:

John "Jock" Campbell:
Expert Support
Double Support
Famous

William Gott:
Avenger
Provocator
First Stike

Denzil MacArthur:
Flag Killer
Ignores ZOC

Arthur Allen:
Lightning Attack
Double Attack
Butcher

Hugh Russell:
Double Move
Vigilant
Entrenchment Killer 2x

J.A.L. Caunter:
Overwhelming Attack
Double Attack
Provocator

Horace Robertson:
Flag Killer
Unyielding
Vigilant

Iven MacKay:
Sixth Sense
Alpine
Leadership

John Combe
Shock Tactics
Superior Maneuver

George Wootten
Fast Deployment
Ignore Mass Attack
Bunker Killer

Italian Side:

Giovanni Cerio:
Flag Killer
Cheap Replacements

Pietro Aresca:
Unyielding
Provocator

Francesco Argentino:
Lightning Attack
Readiness

War Stories - Fall of Poland:

Aleksander Kowalski:
Double Attack
Vulnerable Attack

Igor Dramowicz:
Scavenger
Overwhelming Attack

Symon Borowik:
Zero Slots
No Entrenchment

Civilian Paszkowski:
Survivor
Resilient
Low Profile
Evasive

Nurse Lewinski:
Survivor
Sixth Sense
Low Profile
Evasive

Commander Balinski:
Survivor
Double Attack
Tank Killer
Evasive

Lieutenant Urbanowicz:
Survivor
Thorough Preparation
Fierce Fighter
Evasive

Thanks to kdrushal and Redeyes for some of the traits