If you listened to the latest Co-Opticast, you'll know that one of the things I talked about was the expandability of Left 4 Dead, specifically in the case of "zombie scenarios." I talked about the fact we'd probably see a Dead Rising style mall, and sure enough, there's one already in the works based on the Dawn of the Dead mall.
Website L4DMods.com will be the exclusive home of the map, one that's actually been in the works for fives years. The creator promises the map will be ready REAL soon. I can already see the hordes of zombies flowing out of the Gap in their tight jeans.