On the Internet, check out:

World Wide Web:  http://www.why.com/ultima/
FTP:  ftp://havoc.why.com/pub/ud/
      ftp://sneezy.caltech.edu/pub/ud/

Internet Relay Chat: Undernet (such as server us.undernet.org) channel #udic

Usenet Newsgroup: alt.games.ultima.dragons