The Fatal Frame games make me crap myself! The atmosphere is so tense that I sometimes find myself hesitating while moving, or standing still outside a room that I'm just too nervous to enter. IMO they are scarier than both Silent hill and Resident Evil.

Also, I find that in horror games sound is the main factor in producing scares. It's for this reason that I play them using headphones with the sound whacked up to a very high level. BELIEVE ME! Doing this all but ensures a nerve shredding experience. It literally multiplies the scare factor.