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.
Half-Life Black Mesa
A relentless team of fans have finally released Black Mesa a remake/upgrade of the first Half-Life game from Valve.
Valve's Source Filmmaker
Valve have announced the Source Filmmaker, their tool for creating animated films in a very intuitive way.