Depends if you want to be scared or sickened:
Scared:
Depending on your taste I like the 80's slashers, NOES, Halloween etc
From asia I like Audition and Battle Royale (though the later isn't that scary), I wouldn't bother with Ringu though, terrible film. The Grudge is good though, and the Eye wasn't half bad.
Night of the living dead is quite a good flick, though I would steer clear of the rest of the series (the remake of Dawn of the Dead is good).
28 Days Later was a good watch, haven't seen the sequel though I hope it lives up the original. Wickerman is worth a watch aswell.
Sickened:
I could not sit through Salo/120 days... it really was a gross/demoralising film (I turned it off at the 'nails' scene). I thought a lot of the violence was very gratuitos (sp?).
Last house on the Left is a good effort by Craven as his first feature, I think he's one of the best directors in horror (rent out scream!).
Ichi the killer (if you can get the uncut version) is definately one to watch, I haven't seen the cut version so I couldn't comment on it, but the uncut version is gory and hard to watch in lots of places, the story line is superb.