http://kotaku.com/5096479/dawn-of-the-dead-mall-coming-to-left-4-dead
modded map.
from an interview with FiringSquad
QUOTE
Q. FiringSquad: After the game is released on the PC will there be any additional content released for Left 4 Dead as has been the case for Counter-Strike Source?
A. Michael Booth: Absolutely. We already have ideas for additional missions, features, and content that we hope to ship in future releases/updates to Left 4 Dead.
In addition, an L4D-specific update will be made to the Source SDK so members of the community can make their own missions, characters, and L4D MOD content.
all this is from the forums at Gr.net
i may get it later :0