The Shining
The Thing
Alien
The Evil Dead
aaand I think I'll have to agree with dammage79 on Event Horizon. That movie terrified me as a kid. Apparently there's a director's cut with more hell scenes that were only used for fractions of a second in the film, but it will probably never get released sadly.
Here are some stills from it though:
http://io9.com/new-images-suggest-ev...som-1161668923
Honorable Mentions:
28 Days Later
The Conjuring
The Ring