I also recommend The Binding of Isaac. It's $2.49 right now, and it is my favorite indie game of the year. It mixes old-school Zelda dungeons with roguelikes, twin stick shooters, and nightmarish imagery. It was made by Edmund McMillen, who is half of Team Meat. Please buy this game, because I want to see more things being made by him. He's a really cool guy, and I've been talking to him on and off for a while now about some stuff that I'm planning.