Eek!

[Axolotl]

Scariest game I've ever played was Theif: Deadly Shadows, Cradle level alone puts it there.

 

[Jursa]

Recently finished silent hill 2 and gotta say... compared to it, F.E.A.R is more like a walk in the park on a sunshiny day. Condemned was creepy in a jump out smack you on the head with a knife/axe/shovel/pipe/board from dark or corner which made you hug the block button, while silent hill would often leave you without a monster for an hour, but throw in the sound effects and make you feel like you're being watched the whole game by something playing with you like an ant below a magnifying glass. Resident evil wasn't as much about fear of enemies as fear of small inventory space and fear of ammo lack.

 

[Lukeje]

Condemned. I can't remember which one I played, but the part with the mannequins... it scares me to talk about it. That whole game made me feel sick from terror. I haven't forgiven my friend for making me play it with headphones. It wasn't even a cheap jump-out-at-you scare. It was awful. I haven't played a horror game since.
*shivers*

EDIT: Dammit, black lincon! Beat me by... two whole minutes? My internet is slower than I thought.

Your fear is made all the more apt by the fact that your avatar is Courage the Cowardly Dog...

 

[Supernovajake]

Scariest game I've ever played was Theif: Deadly Shadows, Cradle level alone puts it there.

Ahhhh, the horror of the pixels!!
EDIT: Err...oops meant to quote the guy that said Doom 1. Sorry about that

 

[haruvister]

The original Doom was terrifying at the time. The sound of those pink demon things barking was the sound of evil programmers plotting to turn out the lights any... second... now...

I found some moments in BioShock kind of unsettling, too. The first run-in with the incendiary splicer at the start of the Arcadia level, with the grim music lifted from The Shining: brilliant.