Absolute Horror Film Forum

When I was a kid, I saw The Exorcist. I laughed. (Then I read the book. Terrifying). While there has probably never been a film that made better use of contrast of complete silence with loud explosive noise, it wasn't the scariest for me. The second Exorcist movie had only one redeeming quality (well, actually, two), and that was that Linda Blair was a full-grown woman.
But The Exorcist 3 was one of the most chilling movies I've ever seen. If you have never seen it, you should.
"In The Mouth of Madness" starring Sam Neil wraps some very disturbing special effects around the common fear of insanity.
The original "Halloween" was the best in the (oh- I dunno) "slasher" sub-genre. But I would include the first "Nightmare on Elm Street" as perhaps of equal chill factor.
"Prince of Darkness" actually gave me nightmares.
The Steven King re-make of "The Shining" included some of the scariest elements of the story that Kubrick had excluded.
The re-make of "Dawn of the Dead" .
"The Ring".
"Gothika"
"13 Ghosts"
In the 80's, there was a movie (I can't recall the name), where a town doctor was secretly medically reconstituting people in the town as they died (and killed those still living so they could be a part of the dead dependent on the doctor). The town sheriff finally discovers what's going on, and simultaneously discovers his wife (one of them) had killed him and he needed a treatment from the doctor to keep his flesh from decomposing. I hope somebody remembers the name of this movie.

"Salem's Lot"

I could probably go on. I will say that a lot of movies that are called "scary", I find entirely-too-predictable to be frightening.