I forgot to mention The Orphanage... what a great movie.
Thank you. I came into this thread just to mention that and leave. Not that my opinion matters much as I don't watch a lot of horror films.
And while it may not count as a horror film per se, the Pale Man segment of Pan's Labyrinth
was sheer genius and IMHO quite unsettling.
I think I'll also throw in Antichrist
. I just found that a deeply uncomfortable viewing experience, though I'm sure one's mileage varies here.