There was a similar thread, but it's closed, so I'm remaking it. What's the scariest video game moment?
I nominate The Shalebridge Cradle in Thief 3. Everything else, fear wise as far as games go, pales in comparison to this utterly disturbing level. The rest of the game isn't that scary, but the sheer atmosphere of this level is enough to merit playing it through in 20 minute segments, with pauses in well lit rooms.
Seriously, supposedly "scary" games like Doom 3 and FEAR are like a trip to disneyland compared to the cradle. They use cheap parlor tricks, like in bad horror movies with monsters lashing out at you. But this the cradle is different, it's much more psychological.