As part of the Games with Gold program, Xbox 360 owners who are Xbox Live Gold members can pick up digital versions of Might & Magic Clash of Heroes and Halo 3 this month, for free.
Might & Magic is available today and will be listed as a free download until October 15th, and then Halo 3 goes live for the remainder of the month.
The next set of releases will go live in 2 weeks (1st and 16th of each month), so make sure to grab copies if you have any interest in owning them digitally.