Babylon 5 was an science fiction show, created by Joseph Michael Straczynski, which aired from 1993 to 1998, set aboard a space station of the same name. It spawned several TV movies and the short lived spin-off series Crusade.
The last sign of life was Babylon 5: The Lost Tales in 2007, the first of a supposed series of feature lenght short stories, which by all accounts seem to have been cancelled.

It was an early show to have a large Online presence, but it was mainly limited to the now defunct GEnie Online service, where Straczynski interacted directly with his fans.
There have been and to some extent still exist a large number of fan sites on the Web too, as well as several Usenet groups dedicated to the show, such as rec.arts.sf.tv.babylon5.moderated.
I'll try to provide a list of links to fan sites and wiki's later on.