Microsoft's Games with Gold campaign is currently letting Xbox Live Gold members download the delightful Might & Magic: Clash of Heroes for free, but later this month it's a blockbuster that is made available for free - namely Halo 3.
Once the fastest selling video game of all times, Halo 3, is by many seen as the highlight of the series. If you haven't played it there's no reason why you shouldn't download it now that it's free. The promotion ends on October 31.