At long last, new Left 4 Dead 2 DLC is almost here. Yesterday Valve confirmed via the official Left 4 Dead blog that Cold Stream, the user mod turned official campaign, is almost ready for release. Including a whole new map as well as ports of Blood Harvest, Crash Course, Cold Stream, Dead Air, and Death Toll, the DLC will be available on Xbox 360, with a final build to be released on Mac and PC.
"Other surprises and details" are promised for the upcoming weeks before Cold Stream's debut, which is now set for July 24, 2012. Personally I'm hoping one of those surprises is that the DLC is free.
Cold Stream Release [Left 4 Dead Blog]