Name the scariest movie you have seen?

Anaconda?! I don't know if I'd pick that one . . . If Anaconda scared you, you would probably run screaming from its sequel, Anaconda: The Hunt for the Blood Orchid, or even Snakes on a Plane! Give me a good satanic horror film, like The Exorcist or Rosemary's Baby. That's what scares me, if done right!