Hmmm, System Shock 2 was awesome. Great atmosphere. Those crazy midwifes gave me the absolute creeps

. I remember late one night I was playing with my sis as spectator and I was being persued through the darkened corridors by those evil spider creatures, horribly low on ammo. I ended up in a dead end and turned around and emptied the last of my clip into them and they are all over me. I'm screaming my head off, my sis is screaming "Throw the gun at them, throw the gun at them" when the light switches on and my mum tells us to shut up and go to bed. Hehe.
I found The Suffering quite creepy, the creatures with blades for arms and legs where freaky.
Despite what everyone says I thought RE 4 was pretty scary, though I never made it as far as the castle.
An old game called Sanatarium had a really spooky vibe.