These free games from Ubisoft are pretty good but unfortunately they are ad-supported and I've heard from people that the ads in these games are quite annoying.
Here's a list of the free Ubisoft games + download link:
Far Cry (2.7GB)
Price of Persia: Sands of Time (1.15GB)
Tom Clancy's Ghost Recon (543MB)
Rayman Raving Rabbids (1.3GB)
P.S.: I heard that if you use Fraps you won't even see any ads at all..