Honorable Mention to Fatal Frame.
Sure, a game about young Japanese girl who "kills" ghosts by taking their picture with an old-timey camera sounds kind of lame, but oh no. Playing this game in the dark, at night, with the surround sound cranked up is like staring at the sun -- you can't help but do it, no matter how much it hurts.
Scariest. Game. Ever.
And to think I never played the sequel yet. Sometime I really think I must hate myself.