Starting October 1, 2013 Xbox Live Gold members can download Might & Magic Clash of Heroes for free until October 14th. Normally a $15 download, this puzzle game was originally created for the Nintendo DS then ported over to XBLA.
Then, starting on October 15th, Halo 3 will be available for free for Xbox Live Gold members until the end of the month. Halo 3 is normally a $15 download.