We have known for quite a while know that Valve had plans to release new content for their zombie shooter Left 4 Dead. Today we got the first concrete info on those plans from Valve. This spring valve will release the L4D Survival Pack which will add a new multiplayer mode for the game (Survival) along with two campaigns for the title's Versus mode (presumably the two missions in the original game that didn't support Versus mode out of the box).

Valve also plans to release a new retail collection this spring, labeled the Critic's Choice Edition, that will include the original game with the new content. Valve also intends to release their SDK mod tools for Left 4 Dead this spring as well which will let anyone made new missions for the game.