Keeping its promise, Valve has pushed out new downloadable content for its popular zombie shooter, Left 4 Dead. Called "Crash Course," the update brings a new campaign, which falls between the events of "No Mercy" and "Death Toll," and features fresh locations, dialogue, refined item spawning and more. As we've noted in the past, the DLC is available to PC gamers for free via Steam, but owners of the Xbox 360 version must cough up 560 Microsoft Points -- about $7.

Additionally, to celebrate the release of Crash Course, Valve is offering a 50% discount on the PC version of Left 4 Dead, which brings the game down to $14.99. This promotion expires on Saturday, October 3 -- so get it while it's hot. If you can hold off on the zombie apocalypse, Valve is preparing to launch a demo of Left 4 Dead's sequel, Left 4 Dead 2. The completed title will hit store shelves on November 17 with a slew of new features.