rec.games.corewar on Google - since it's formation in 1991, the newsgroup has provided a valuable forum.
The #COREWARS IRC channel on irc.freenode.net is the official channel of the Corewar community. Daily events have been logged since 16 May 2009 in the irc-logs directory.
The KOTH.org #COREWARS IRC channel has moved to irc.koth.org port 6669. Daily events have been logged since 14 Sep 2005 in KOTH.org's irc-logs directory.
ICC 2004 - the 20th Anniversary of Corewar Meeting organised in Berlin by Christian Schmidt, July 2004.
Jakub's IRC Logs - old logs of the happenings in #COREWARS covering the period Mar 2003 to May 2004.
Corewar Web-Forum [use rec.games.corewar instead]
Koth has a mailing list echoing rec.games.corewar. To subscribe, send an email to listproc@koth.org with a body of subscribe corewar-l (name).