Here's the list of free games for xbox live gold members:
The Incredible Adventures of Van Helsing
Availability: December 1 to 31
Thief
Availability: December 16th to January 15th
CastleStorm
Availability: December 1 to 15
Sacred 3
Availability: December 16 to 31
Operation Flashpoint: Dragon Rising
Availability: December 16 to 31
The Incredible Adventures of Van Helsing
Availability: December 1 to 31
Thief
Availability: December 16th to January 15th
CastleStorm
Availability: December 1 to 15
Sacred 3
Availability: December 16 to 31
Operation Flashpoint: Dragon Rising
Availability: December 16 to 31