Moonlight Butterfly said:
The original FEAR is quite creepy so I've heard.
I'll admit, it did make me not sleep for a few days when I played the demo. Then again, at that time, I was scared easily, I thought "pft... how could a game be scary?", and played it home alone, at night, with all the lights off. Game was still pretty scary the first time, but if you are into horror a lot, it might not seem to bad.
Not sure of any free games besides Slender, which I guess is supposed to be scary? I definitely second Amnesia, though. That and possibly the Penumbra series, too.