I Can't Escape is an interesting little game. I'm not sure if it really qualifies as horror...and it is very, very short. But it can be played directly in the browser, so why not give it a quick look while you're here?
Personally, I found it rather scary, at least on my first playthrough. The mechanics it uses to evoke a feeling of increasing helplessness and panic are simple and don't engage for very long on their own, but they work quite nicely as an experiment of sorts...maybe inspiration for a bigger and more complex game.
(If it doesn't work, make sure your flash plugin is up to date and that hardware acceleration is activated, since it's in 3D)