WE'RE PLAYING URBAN FLIGHT TODAY AUG/9/2012If you're looking for custom maps, here.
http://www.l4dmaps.com/That site also has mods, skins, textures, voices, etc. So you can do a lot more. My friends and I use it for campaigns mostly. Check it out, make an account, give them your credit card number, lose all your money, rinse and repeat. I'm not telling you where I got the radio voices mod from. :D
For installing mapsC:/steam/steamapps/common/left 4 dead 2/left4dead2/maps
For installing .vpk filesC:/steam/steamapps/common/left 4 dead 2/left4dead2/addons
Here's some maps and stuff you guys should try out.Dead Before Dawn: http://www.l4dmaps.com/details.php?file=7774 (I haven't played it)
Silent Hill: http://www.l4dmaps.com/details.php?file=14814 (Dark, tough, and takes forever. co-op only)
Haunted Forest: http://www.l4dmaps.com/details.php?file=6923 (Best played with "Darkness Falls" mod)
Death Aboard 2: http://www.l4dmaps.com/details.php?file=4861 (I haven't played it)
Urban Flight: http://www.l4dmaps.com/details.php?file=6905 (This was a lot of fun with my friends)
MPC is a tank: http://www.l4dmaps.com/details.php?file=14441 (Re-Skin for tank)
MPC Icon: http://www.l4dmaps.com/details.php?file=19214 (Tank icon)
I'll Be Bahk: http://www.l4dmaps.com/details.php?file=18266 (Tank theme, never tried it)
Amurica: http://www.l4dmaps.com/details.php?file=13871 (It's for the witch)
There's also a ton of re-skins for guns, a lot of them change the whole model.