Portal: Survive! is a live-action short film based on the Portal game, and its tie-in comic Portal 2: Lab Rat.
Team Fortress 2 - Mann vs. Machine
A robot faction is introduced into the Team Fortress 2 equation, via this amazing new trailer by Valve.
Valve's Source Filmmaker
Valve have announced the Source Filmmaker, their tool for creating animated films in a very intuitive way.