New or old?
Urban Legend (appeals more to the female crowd, but I still think it's a very, very good movie)
John Carpenter's Halloween (who hasn't seen that one, though?)
John Carpenter's They Live (more sci-fi than horror, but still suspenseful and a must-see)
Texas Chainsaw Massacre (original)
May (also for the female crowd more, but still good and creepy)
The Omen (religious movie)
Drag Me To Hell
The Exorcist (of course)
Paranormal Activity (AMAZING movie, however, there are mixed reviews)
SaW (original. I liked it because it wasn't a gore flick)
Those are some good ones, both newer and older.