Add to the list if you know of others. I can also add some description to the sites if you have info on any aspect of those listed.
VDiplomacy: http://www.vdiplomacy.com/
WebDiplomacy: http://webdiplomacy.net/
PlayDiplomacy: http://www.playdiplomacy.com/
Backstabbr: http://www.backstabbr.com/
Diplomaticcorp: http://www.diplomaticcorp.com/
Bounced: http://www.dipbounced.com/
Diplomacy.ca: http://diplomacy.ca/vforum/index.php
Stabbeurfou: http://www.stabbeurfou.org/
VDiplomacy: http://www.vdiplomacy.com/
WebDiplomacy: http://webdiplomacy.net/
PlayDiplomacy: http://www.playdiplomacy.com/
Backstabbr: http://www.backstabbr.com/
Diplomaticcorp: http://www.diplomaticcorp.com/
Bounced: http://www.dipbounced.com/
Diplomacy.ca: http://diplomacy.ca/vforum/index.php
Stabbeurfou: http://www.stabbeurfou.org/