Portal, the best game of 2007. Entitled Portal: First Slice, the demo features more content than the normal demo, and is available free to all NVIDIA customers through a new partnership between Valve and the hardware manufacturer.
The offer is accessible through Steam, which will scan your computer to confirm the presence of NVIDIA hardware before making the offer available (creepy). Game|Life also reports that in addition to the Portal: First Slice, demo, NVIDIA customers can also download Peggle Extreme, Half-Life 2 Deathmatch, and Half-Life 2: The Lost Coast for free through the same offer. Not too shabby.