I agree with everyone who has said Eternal Darkness, That game is insane. Everyone interested in games designed to scare shoiuld check out Sadness coming out for the Wii.
My scariest game moment was when I was playing Doom 3. I have bose triport headphones that blocks all outside sound. I was sitting in the dark at my computer playing and my wife comes home from work. I was in the section where it's completly dark and the monsters are jumping out of the rafters, all you have to see them is a flashlight, which is scary enough as it is, just then my wife just lays her hand on my shoulder to ask me how I am and I jumped so high, it scared me silly, it was great. We still laugh about it today.
when i was playing doom 3 (not THAT scary but it had its moments) and i was in a vent or something and i could hear fast breathing, and it sounded like it was coming from everywhere and getting closer lol
oh, and also when you are going down that hallway with the blood writing on the walls, and there is that chainsaw dude that you can sort of see in the distance, but when you get close, he disapears. and when you see him he is just...standing there...(then he tries to kill you lol)
