Dead Rising 2 and Dead Rising 2: Case Zero
These two games are free for the month. They are pretty much zombie games, but a bit more unique. You are basically stuck in a theme park and a mall, and you have the ability to create and combine many different items in the game. You can either make this game humorous and create hilarious weapons, or go the generic route and just maul down the zombies. Pretty good game if you ask me, and hey, it's free!