Absolutely Theater 
Forums dedicated to the discussion and operation of all things theater.
http://groups.msn.com/AbsolutelyTheatre/Talk About Theater
Theater discussion forums include a variety of topics.
http://www.talkabouttheatre.com
Theatre VOICE
Audio driven discussion forum in which theatre critics from across the UK press talk about London shows.
http://www.theatrevoice.com
Community Theater Green Room
Discussion boards with topics including theater resources, articles, how-to's, directing, props, set design, play reading, and humor about acting.
http://www.communitytheater.org/discuss/default.asp
Educational Theatre Association
Discussion boards relating to the theatre and acting. Topics include scripts, technical matters, performing arts education, and the theatre for life advocacy campaign.
http://www.edta.org/connections/discussion.aspx
