Valve are introducing the Perpetual Testing Initiative for Portal 2 with this new amusing trailer.
Portal: Survive! is a live-action short film based on the Portal game, and its tie-in comic Portal 2: Lab Rat.
Valve's Source Filmmaker
Valve have announced the Source Filmmaker, their tool for creating animated films in a very intuitive way.
Dota 2 - Cinematic Trailer
Valve have released an action packed cinematic trailer for their new game, Dota 2.