Somehow I found the Hollywood remake of "The ring" quite scary and the Japanese version mostly boring, althouggh that's one of the movies that's only good the first time you watch it. (Like "The others" or "Blair witch project")
The last movie that had a big impact on me was "Donnie Darko", which is not a horror movie at all.
I watched it alone in a dark room late at night and I had no idea what the movie was about (I just got it from a friend that told me that it was good and I should watch it)
So, there I was sitting..... and nothing could have prepared me for Frank, that 6-foot-tall bunny rabbit.
Sidenote: All good horror flicks have to be watched alone, in a dark room, preferably at night. All the scary-ness is lost, as soon as another person is there with you, which somehow reassures your subconciousness that it's just a movie you're watching.