Like many others, I've watched enough horror/slasher/thrillers to no longer be scared or surprised by the majority of them, as they are mostly predictable (yes, Drag Me To Hell, I'm talking to you

), but I do have some that genuinely chill me:
An American Werewolf in London - now I must emphasise that, watching this again now, I find it entertaining, ridiculous but not scary, but it took a long time for me to be able to rewatch it, after a viewing of it when I was about 6 (horrible brother letting me watch it!) set me up with nightmares for a couple of years. So I still remember it as a scary film, even though it's not anymore.
But ones that I still find pretty chilling are:
The Others
The Ring (US version) - Samara crawling out of the tv is one of the creepiest film scenes of recent years (although when I rewatched it with my ex, he ruined the atmosphere by laughing throughout it - it somehow didn't seem as scary with him doing that!)