I'll recommend some movies but the problem with this sort of question is:
A) Everybody has their own definition of scary.
B) Most people (usually the younger crowd) don't have an appreciation for older horror movies that are/were considered scary due to newer horror movies that are nothing but a gore fest. Most people are desensitized to that sort of thing now.
Psycho
The Exorcist
Halloween
Halloween II
The Shining
IT
Well my favorite is Shining, but that might be too soft for you. Try Cannibal Holocaust. I would not watch something like that, but it seems pretty hard.
I really think it all does depend on your opinion but do you want a funny - scary? because a good one is Shawn of the Dead. I was laughing in my seat the whole time *It's an English Movie*