For the month of July, Xbox 360 owners who are also enrolled in the Xbox LIVE Rewards Program can purchase any two XBLA games priced at 800 Microsoft Points or more and will receive 200 Microsoft Points back for free. There are currently nearly 400 XBLA titles in the marketplace appropriately priced for this promotion.
The Xbox LIVE Rewards Program is available to all Xbox LIVE Gold subscribers and is completely free to join. It rewards gamers with loads of free Microsoft Points simply for purchasing certain content and giving feedback via a short monthly survey.
Here is the list of eligible games.
http://marketplace.xbox.com/en-GB/Games/XboxArcadeGames