For best western horror movie I'd say Halloween. I do like the fact that the "monster" of that movie is only human instead of some spirit/undead/random monster. However I have watched a lot of TV and movies as well as reading a lot of books so most western stories are predictable and cliched to me forcing me toward weirder media. Thus I explored Japanese horror and came across Gyo (warning: do not watch this movie unless you're already accustomed to and comfortable with Japanese horror and Japanese culture in general) which has become my all time favorite horror movie.
Until the end..when they tried to explain it all with that dream crap
Honestly, in my opinion, it's hard to find good horror movies. Most of them turn out to just be suspenseful movies (one was mentioned earlier, Sixth Sense) and a lot of others try to pass itself off as a horror movie through cheap scares (the kind that make one jump, and leaves it at that)
What I like from my horror movies are the possibility of it happening (The Bad Seed, for example) or a lack of explanation (Blair Witch Project).
I'd love to get a chance to make my own horror movies, I've got a pretty twisted mind, I think I could do quite well. Especially a movie based off of an image I randomly imagined one time (demon/creature thing, tall..torso and head is seen out of the 2nd story of a house, face seems to be like a mask on the head..though is actually the face, long and pointed nose, mouth sewed close right in the middle...left and right sides are still open however, round eyes...right one with a lot of dried blood under it, somewhat long black hair..goes to about halfway at neck..hair going from back of head is straight..hair going from left and right side is frizzy, arms so long they reach the ground...completely black...6 fingers...pointed at the tips but not sharp, body composed of random black and red splotches, when looks directly at person..the person hears a faint piercing scream that gradually gets louder..but only when looking at the creature in the face and being looked at back, the creature does not attack ferociously...but circles the house trying to reach in for the person at random times)
I dunno if it's horror or just scary, but I love Signs. Recently saw The Blare Witch Project, it freaked me out, but it's pretty awesome. As for The Shining... all I can think of is "Here's Johnny!" xD
If anyone has seen "The girl next door" they will know it is really messed up if anyone hasn't seen it it's on lovefilm but be warned it is really disturbing and sick.