Two games that I can surely recommend are Super Mega Baseball: Extra Innings and They Bleed Pixels.
Super Mega Baseball: Extra Innings is everything it should be when it comes to an action based baseball game. It plays well. It can be challenging. However the nice thing about this game is the different sort of art style. It is retro a la games on Super Nintendo and even Nintendo.
As for They Bleed Pixels it is a Super Meat Boy-like game with really good controls and when I saw TotalBiscuit’s video on it I knew I’d definitely keep the key for myself.
Other game included … The Deadly Tower of Monsters which I might not keep the key for myself is a game to me that has a camera that just will make me sick at times. Too each his own though.
Anyway this is a pretty nice $1 tier and of course you can pay more and get more games and the other nice part is you give money to charity. : )