Valve have announced the Source Filmmaker, their tool for creating animated films in a very intuitive way.
Valve have created Expiration Date, a 15 minute animated short featuring all the Team Fortress characters.
Portal: Survive! is a live-action short film based on the Portal game, and its tie-in comic Portal 2: Lab Rat.
Portal 2 - Perpetual Testing Initiative
Valve are introducing the Perpetual Testing Initiative for Portal 2 with this new amusing trailer.