I don't care if it's somewhat dated, The Excorcist still scares the crap out of me, even 30 years after the first time I saw it. I can't even watch clips of it now.
Witchboard (from the 80's) scared me and I still think it holds up.
Some movies like The Hills Have Eyes I find to be quite psychologically disturbing, but not scary. I'm uncomfortable in the same way I would be watching any rape scene, but I don't consider it "horror" or "scary."
Honestly, I'm trying to remember the last movie that actually "scared" me (as opposed to startled me- by things jumping out of closets and such), and I can't remember when! It's been THAT long! Edited to add: Final Destination actually did scare me

. Edited to add even more: Ok, now that I said I can't remember, I remember! Signs (with Mel Gibson) scared and fascinated me!