First off, the humble bundle is going on right now, if you're newer to PC gaming, you may not know of it yet. http://www.humblebundle.com/ Pay what you want for a good number of games, they always add a couple before it ends, too. (Of course it's for charity if you so choose, so paying a decent amount is more fair to them.)
Any of the Trine series: http://store.steampowered.com/sub/16532?snr=1_8_4__501
Torchlight 2: http://store.steampowered.com/app/200710
If you hadn't played it on 360, Bastion: http://store.steampowered.com/app/107100
Also, like the poster after me said: Check Amazon deals atm, they have some good stuff going on. And most of them redeem to Steam.
