Penumbra and Cryostasis are two really awesome titles. Other good ones are Barrow Hill, Scratches, and The Lost Crown. Anyone else know of games like these?

ElastoMania freaks me out...
But seriously, I think you named them all. There are only a few really good ones.

Back in the shareware days, "The Last Half of Darkness" scared me a lot as a kid. Shivers up the spine, stop playing and hide under the desk.
I'm not sure how well it has held up, and there apparently has been a few remakes since it's release, but they don't have the same scare factor (either that or being an Adult, I'm harder to affect).
+1 for Scratches though.

I want someone to make a game based on eighties slasher flicks where you play either a victim trying to survive against an AI killer and keep as many of your friends alive well while getting naked and doing stupid things, or you can play as the killer and hunt down the AI controlled stupid hot naked people with various objects. Of course you'd be expected to freak them out first if possible.

*Teenager walks into deserted house late at night and leaves the front door open*
"Billy? Billy you here? I'm going to get naked and take a shower okay? Don't lock the doors or anything, I like the moving air."
:P

Hehe, ElastoMania is absolutely brilliant! And highly addictive!
Oh yes, this could be such an awesome game. You'd be laughing all the way through. They'd probably have to make a number of levels based on different movies though, otherwise it'd be much too short.

I found "5 Days A Stranger" quite creepy.

Oh, yeah, you're right! I totally forgot about Yahtzee's horror series. Those were made before he did that whole Zero Punctuation stint. I used to be an aspiring AGS developer, and his games used the engine extremely well (his and the Ben Jordan series by Grundislav).
The closest I think you'll get to that dream is Clock Tower, though there's no nudity and you can't play as the killer. Everything else you talked about, though, pretty much describes Clock Tower.

There's an adventure game that's on the horror side of things. It's called Prodigal. Completely free.
Link to the game.
Have you also tried Fatal Frame for PS2/Xbox?? I know it's not exactly indie or anything but it's still survival horror.

"The White Chamber" is also quite disturbing at times.

Indie, freeware, horror, awesome.
Missing.

Lost in the Nightmare was pretty damn good when I played it years ago. Just remember to apply the latest patch as the initial translation was god-awful and there were a few game-breaking bugs.
It used pre-rendered screens from the Half Life engine to create a Myst-like horror game.

Those screenshots...damn...
Myst-like horror game? I'll truly shit my pants, then, since I was scared to death when I was seven, playing the original Myst. It always seemed to quiet, like someone was about to sneak behind me and stab me.

My idea was that the levels would be themed based on classic slasher flicks but be procedurally generated, as would the victims and possibly the killer. Or you could make your own.
TheChesse33: I've heard of Clock Tower. I'm pretty sure it never came out in the US though right? It also doesn't seem like it had the 80s slasher vibe I'm talking about. Specifically, the vibe Soduka so effectively captured with that post.