http://store.steampowered.com/recommend ... app/218410
Defender's Quest: Valley of the Forgotten
It's a cross between an oldschool turn based RPG, in real time, and tower defense. It's easily the best $5 I've ever spent on a game (sale price until the 5th)
http://store.steampowered.com/app/113200/
The Binding of Isaac
This game is hard as fuck. It's like Zelda(NES) in a bullet hell sort of mode. It's creepy and weird, and doesn't tell you much about what things do, but you can figure it out. (Or look at the wiki...)
I'll add more as I get time to try out the other great games on sale.