Jaws, when I first saw it, I actually got out of my seat and hid on the floor! At that time, that was as scary as it gets. Then the Omen, Exorcist. Read the Amityville horror, it is way more scary than the movie. Any of Stephen Kings books are better read than watched. There is so much more to the story than is on the screen.
Saws and Paranormal Activity, cuz Saw is just pure gruesome, and makes u want to know wht happens next, but some people don't want to, and paranormal activity is like the kind you don't want to see alone in the dark, and also like the kind you plug your ears and cover ur eyes.