Valve have created Expiration Date, a 15 minute animated short featuring all the Team Fortress characters.
Team Fortress 2 - Mann vs. Machine
A robot faction is introduced into the Team Fortress 2 equation, via this amazing new trailer by Valve.
Meet the Medic - Behind the Scenes
See outtakes and learn about Valve's creative process in this behind the scenes article for their Meet the Medic short.
Portal 2 - Boots
The science of the boots used in Portal 2 is explained in this latest video from Valve.