Some of my favourites have already been posted but here goes:
The Legend of Hell House
Child's Play 1
Friday 13th 3 & 4 (The rest are a bit shite, those two were genuinely scary)
Evil Dead 1 & 2
Jaws (The bit when Ben Gardener's head pops through the hole in the bottom of the boat still scares me now)
Halloween (The first one, another absolute classic
)