This is more or less for Brandon (Although it can apply to 1 or 2 more people.)

Custom Maps:
Instructions for Installing: http://www.l4dmaps.com/install-maps.php

Payload Hoodoo: http://www.l4dmaps.com/details.php?file=5932
An imported tf2 map, supports survival and coop.

Night Terror: http://www.l4dmaps.com/details.php?file=5845
A variety of maps that stretches from the Haunted House from Disneyland, to the Underground Kingdom of Moria from LOTR.

Questionable Ethics: http://www.l4dmaps.com/details.php?file=9773
A puzzle map for L4D2.