Is there anyone out there who plays RtCW: ET? It is a 100% free, standalone multiplayer game. They were gonna make it an add-on for Return to Castle Wolfenstein, but... they gave up. Thus they released what they had done to the public. Don't let the uncompleteness idea confuse you; it's not like this game has missing textures or sounds or anything. It is absolutely wonderful. I've been playing it for over a year now, and there is never a dull moment. Playing head to head against human players... Thousands upon thousands I have fought. And while I consider myself a pro (not the best am I!), there is still much to be learned. I give this game a 10/10 rating.
http://enemy-territory.4players.de:1041/ for the game and patch.