I'm going to recommend what I recommend every time somebody asks this, or a question like this, Company of Heroes. It's an awesome game, and cheap enough that you'd still have another $10. If you're not into RTS games it's not for you though
Judging by the roster of games still on sale for the next 20 hours id suggest you should pick:
-Torchlight 2 (ARPG) - dungeons and looting and lots of particle effects...good co-op game -Arma 2: combined ops (Military Sim) - the game by itself is fun, but the bread and butter right now is all about DayZ -Borderlands GOTY edition (although if you already own number 2 you might as well pass.)