www.churchsoundcheck.com
ChurchSoundCheck. My personal favorite. Started as a mailserv forum, and has now expanded to Facebook as a fan page. You can find a link to join the forum here. You can find the Facebook fan page here.
www.audioforworship.com
AudioForWorship. Another good source of information for church-related audio.
www.kodachrome.org/salt/
Sound And Light Training. This is an excellent resource for practical learning. It is geared towards church sound and light systems, but the principles easily convey into other contexts.
www.soundfirst.com/technical.html
Ray Rayburn’s Technical Page. Ray Rayburn is a master sound/audio engineer and this page has lots of different bits of technical information that you may find interesting.