@ Bear - Some horror that I love, probably more to add:
The Shining
The Exorcist
Evil Dead 1,2 & 3 (okay, more comedy)
The Dawn of the Dead (1978 version)
Ring (1998 Japanese version)
The Fly
The Thing (Jon Carpenter version)
The Wickerman (1973)
A Nightmare on Elm Street
Psycho
Alien (arguably a horror over sci-fi)
The Descent
28 Days Later
I don't think I have watched a horror while high on LSD actually, could be dangerous!
I absolutely love The Shining, the music in it really adds to the tension.
The Japanese Ring movie is far more superior than the US version & The Descent is great also.