Valve have announced
the first round of DLC for their zombie shooter Left 4 Dead, as well as a new edition of the game:
The first L4D DLC — dubbed the L4D Survival Pack -- is due for release this spring and introduces a new multiplayer game mode entitled, Survival, plus two complete campaigns for Versus Mode. A Critic's Choice Edition of the game will be heading to retail stores this spring, and will include access to all the content introduced in the L4D: Survival Pack.
The press release also includes mention of a new SDK, allowing creation of Left 4 Dead mods (including new campaigns).