Awesome thread.
The Evil Dead series is legendary in my mind. The first Child's Play terrified me as a child, as did The Exorcist (since I happened to see it at a time when I was actively playing with a ouija board). The Texas Chainsaw Massacre really sits on top of the pile though, and if you don't have at least one version of it on DVD where you can listen to the commentary I would recommend you look into it.
Japanese horror films are pretty good too. The original Dark Water Honogurai mizu no soko kara is really good, as is Ringu, Kairo, and Ju-on. The whole "freaky deaky ghost children" thing can get a bit repetitive though.
Re-animator is a lot of fun too, as are most movies based on or inspired by Lovecraft stories.
So many horror movies to love, so little time.
I can't wait to see more posts.