I've been looking into a fan-made mmo Fallout Online, which seems to have a decently sized community of regular players.
http://fonline2238.blogspot.com/
http://fonline2238.net/forum/index.php?board=1.120
Looks good, as does the various single player restoration packs for Fallout 2.
Guess I should add...I was wondering if anyone on here has played Fallout Online.
http://www.adventuregamestudio.co.uk/yabb/index.php?topic=38736.0