Portal
Though install might be too strong a word. This is the first time I have used it and Steam is royally pissing me off. Is there a reason it stopped my download halfway through in the middle of the night?

Server trouble most probably... They HAVE released something for free after all :D

Starcraft II Beta!
I discovered that I suck!

it's on my account,but not installed

Civ IV complete + Colonization and Eschalon: Book 1 - demo

Civ IV Complete, with the Fall from Heaven II mod. Bought a couple other things I haven't downloaded yet, got to figure out what I can uninstall to carve out some more HD room. Besides, the Luchuirp haven't finished taking over the world yet, I can't install a new game until I win at least one game of Civ IV. ;)

Portal.

Settlers II - 10th Anniversary
I can't wait to try that old legend :)

Portal
Sam & Max Hit the Road

DIRT 2 (from Steam).
Yeah, it rocks...

Blade Runner

Tales of Monkey Island ep1.

Eschalon Book 1. Just started playing it. Fun so far.

AI War, looks good

Dominions 3, an old favorite.