I have several, depending on my mood at any given time. Some chronic favorites:
An American Werewolf In London
Night of the Living Dead
What scares you, and why?
I would say that The Ring and The Grudge scare me. They just seem so sinister without actually making you jump with fright.
Megan, I liked The Ring and The Grudge also, those were cool! I think the original Japanese versions were even better, though. Particulary Ringu, because you never once saw Samara's face. It made here REALLY creepy.
I haven't seen The Grudge 2, is it any good?