Left 4 Dead? Really, you put that game on the list and didn't mention White Day: A Labyrinth Named School, Eternal Darkness, and Fatal Frame? Good god man...
Outlast has a way better chance of being on the list than Dead Space. Although Dead Space does have a strong atmosphere, it loses any fear factor after the first half an hour and instead becomes really fun as you curb stomp and blow off limbs. Outlast keeps you scared right till the last hour of the game.
Have we really become that starved of Horror games that we've devolved into putting games like L4D, Doom 3 and Bioshock on top horror game lists? Reminds me of a video I saw recently