Don't forget to include why it scared you!!!
My first (besides the creepy flying monkeys chasing Dorthy & friends scene in The Wizard of Oz) was Jurassic Park.
I saw Aliens and Predator but since they were in space and a jungle I rationalized it could never happen to me (and yes thats how my 7 year old mind worked). But when the raptors in JP figured out how to work a doorknob that scared the mess outta me, and even more so when they started tryna kill the kids. Plus they were waaaay too good at problem solving!
The last movie that scared me to death was Apollo 18 (and I know many didn't find that scary at all). But when I saw it I was in a theater with two other friends and no one else! Plus the motion camera kept me anxious the entire movie. Not to mention the creepy 'possession' part of the plot.
Thats my two cents!