all mine have been said above.
The thing
Event horizon
The Blair witch (first time i saw it i thought it was sh*t but then the second time it just stuck in your head and creeps you out)
Wolf Creek – another head wrecker, not all out blood n guts but sticks in your head
Salems lot – my cousin was 17 and put this on for me (i was 11) telling me it was a film about lost kids. I sat through it crying, he wouldnt make me lave the room, i had nightmares for years after!
The Ring – the only horror film that has made me reeeeeeally jump, the bit where she comes out the TV!!
28 Days later – another classic, the little bits that freak you out, london streets empty and he motorway blocked off, they way it was shot was great.