My dad took me to see Alien when I was 12. I don't think I slept well for the next couple of years and even as an adult have woken up in the middle of the night after dreaming of that f'ing critter - when I will just say WTF and go back to sleep. Hands down Alien is the scariest movie I have ever seen.
next on the list is The Exorcist. When I was a pre teen that movie aired on HBO. I saw just one shot in the movie that night, a dark presence standing over the girl's bed. I immediately changed the channel because that one shot was instantly scary. I watched it in full some time after I graduated from A&M and that movie cemented its spot as number 2 on my list.
I will go with the TV movie of Salems Lot at number 3. Lots of scary stuff in that one - the kid at the window, the vampire in the dining room....
At number 4 is The Shining. What was it, room 237? That scene still gets me. The little girls are creepy.
The Changeling is #5, with A ball bouncing down the stairs at the end of this ghost story.
The Amityville Horror checks in at #6. The pig eyes, GET OUT!, the purple shape standing in the window behind Margot Kidder...
Poltergeist is #7. I hated that clown. Still do. I watched this as an adult one Halloween night and could not believe how scary this movie remains.
Jaws comes in at #8. Growing up in Lake Jackson, I spent a lot of time at the beach before I saw Jaws; after that, when I was probably 12 or so, I went to the beach maybe twice before leaving the area to come to A&M.
At number 9 is Halloween, a movie I watched late one night on HBO when I was not supposed to. Seeing Michael Myers lurking in the shadows wigged me out.
#10 is a seriously scary movie for a 3-4 year old. I stayed up with my dad watching late night monster movies on probably Channel 39 in Houston. For years all I remembered was a sea creature that was captured, deflated in some kind of pressure chamber, and then re-inflated at some point by a little girl who came in to the room and pushed some buttons on the pressure chamber. Recently I searched long and hard for this movie, not knowing what it was called but just recalling that scene, and finally found it - The Monster That Challenged the World. A truly awful movie but so scary to such a young child.
Honorable mention - Phantasm, The Omen, The Thing from Another World, Dracula (1931), Frankenstein, and The War of the Worlds (1953)