Amazon is running a deal today on Xbox 360 Platinum Hits. Buy two games, get one free! Hard to argue with that value. There are some co-op gems in there: All three LEGO games are less than $20, before the promotion! The original Gears of War, Marvel: Ultimate Alliance, and even Burnout Paradise are all available. Of course there are some single player games included as well, if you want a bit of alone time. If you haven't checked these titles out, now's a good time!
Source: Amazon.com