Starting Saturday (March 1st) Sid Meier’s Civilization Revolution (Normally US $29.99) will be free for Xbox Live Gold members through March 15th .
Then on March 16th, Xbox Live Gold Members can download Dungeon Defenders (Normally US $14.99) for free.
The “Games With Gold” program gives Xbox LIVE Gold Members 2 free games to keep each month. A new title will be available the 1st and 16th of each month.
Source: Major Nelson