Hmmm...I tend not to like horror films too much because the whole throat slitting thing (seems to be a popular death scene choice...) gives me panic attacks. But, since panic attacks are sometimes useful, here are a few of my favorites.
"Haute Tension". I'm not sure what title the English version goes by, but translated it's 'high tension.' It is without a doubt the most brutal, nerve wracking, 'i-feel-sick' film I have ever seen. On that alone, I would generally not recommend it to anyone because it is simply so ...bloody. What redeemed it for me, however, was when I noticed that towards the end, I was sweating, feeling kind of shaky, and was genuinely terrified. It really pulls you into its world and once you're there, it doesn't let up.
"Pet Semetary". Not too scary, but I guess it is something of a classic. Also good is the fact that it has a more philosophical kind of feeling to it; while not explicitly talked about within the film, some scenes deal with the nature of life and death, redemption, freedom and responsibility, etc.
"The Bad Seed". The original black and white one. By today's standards, it's quite tame, but that black-and-white sensibility and near naivete contrasts perfectly with the remorseless, calculating little girl (the bad seed.)
Oh, this is off topic, but I've never been able to figure out what the word "cult" means in context of "cult film," "cult classic," etc. So, what does it mean if a film is say, a cult horror film?
That said, disregard my suggestions if they do not fall in that category. Should've asked before posting, heh.