Everyone seems to be suggesting Japanese horror which I suppose is reasonable, but quality of the horror flicks from HK isn't too bad either. I recommend The Eye 1 or 2.

If you don't mind a bit of comedy in your horror (:rolleyes2 ) then give The Eye Infinity (a.k.a. The Eye 10) a shot.

Any other horror flicks by the Pang brothers are worthy of mention too.