I love them, and I've seen very few. Recommendations, anyone? The more pants-shittingly scary, the better. I haven't been really scared by a movie since the first horror movie I saw (Ringu, for the curious). I want shit that will haunt me and give me nightmares like Sadako and her fucking fingernails as they came out of the TV.
My favourite is The Shining (Kubrick's movie version.) I'm also fond of Ringu and Ju-on. Everything else I have either rated average or not seen.
I haven't seen anything that can compare, but then again I haven't seen much.
I like Kairo. If you haven't seen many other J-horror movies, or other horror movies with a similar style, it should be pretty scary. I also found watching it on a computer made certain parts feel creepier. And as added bonus, on top of the horror, it's really depressing.
"Saw" There are eight of them since 2004. Must see if you like to pants-shit.