With the last Left 4 Dead patch, it enabled third party campaign support... FilePlanet has the first third party campaign, (that I'm aware of) called "Dead City"... it contains 5 chapters and is pretty damn good...

The biggest problem is their is no directions or markings to show you the direction to the next safe house, and I got lost a number of times, another problem is in the Back Alley chapter, you have to all get into an elevator, well that might work in MP, but not SP... the AI wouldn't get in so I had to stop it. Also the last chapter "City Station" is locked, I guess you have to complete the first 4 first... but anyway, anyone looking for another L4D campaign, this one is pretty good.

(download zip, extract, no read me, so you double click the exe to install, no install notification either, in 10 to 15 seconds you'll get the "it's installed" message.)

http://www.fileplanet.com/197327/dow...-Dead-City-Map

Dead City:

Riverside City
Back Alley
Draw bridge (only one I was able to complete alone)
City Plants
City Station (locked)

Here are some screens: