Amazon.com just recently started selling Xbox LIVE Arcade games. You can purchase games at their dollar value (no need to decipher Microsoft Points) and then receive a code which you redeem on your Xbox 360. There's another reason to keep a lookout on the Amazon.com Marketplace for Xbox LIVE downloadable games. You may just find them cheaper.
Right now, Galaga Legions is listed for 800 Microsoft Points ($10) on the LIVE Marketplace, but if you look it up on Amazon.com, it's half the price at $4.97. That's a nice deal for the re-imagined and upgraded Galaga game.