The Thing is a big one for me. I like the isolation and distrust.

All time favorite Horror List:

Night of the Living Dead (Both Original and Remake)
Dawn of the Dead
Day of the Dead
Land of the Dead
Shaun of the Dead
28 Days Later
Return of the Living Dead
Dead Alive
Halloween
In the Mouth of Madness
The Thing
Cabin in the Woods
The Evil Dead
Evil Dead II
Army of Darkness
Terror Train
It Follows
Scream

I could go on for days and I'll kick myself later for ones I forgot to add.

Avoiding any prior listed favorites-

Movies/TV:
-Jacob's Ladder
-Dark City
-the Shining (as a film; Steven King as an author is not my favorite)
-Master's of Horror Series; particular the unaired 'Imprint'- very disturbing
-Rob Zombie films\remakes

Literature (often film adaptaions exist but vary in delivery):
-Weathering Heights- Emily Bronte
-the Witch House, the Mountains of Madness, the Lurker at the Threshold, Pickman's Model- H.P. Lovecraft stories
-The Road - Cormac McCarthy
-Saga - comic book series

Video games of worthy mention:
-the Evil Within
-Bioshock
-Twisted Metal Black
-Dead Space