First Halloween or April Fools Day (1984 i think)
The first SAW, is remarkable! I absolutely love.the story line, and moralled ending...
"Pet Sematary," ba<x>sed on the novel by Stephen King. To quote a character in the movie: "Sometimes dead is better."
There's also one I mentioned awhile ago on here called "The Mephisto Waltz," may not be easy to find, tho worthwhile to look!
A Clockwork Orange, dystopian horror
Yellow Brick Road
you'll enjoy it, watch it in the dark ;)
'Knife Edge' was great, though it was more of a thriller than a horror.
Try The Entity
that movie freaked me out when I saw it as a teenager; try also The Sentinel and The Legacy