The only ones that I (frequently) post at are caving ones www.caves.org and a Utah based caving forum of which I am one of the administrators. An infrequent one I post/read is www.kevinswatch.com which is devoted to fantasy litrature and primarily deals with the books where a quote is the first of my signature.
I probably LIVE on MT most of the time. Because MARTIAL TALK RULES!!!
I used to post on about a half-dozen fora pertaining to my old church. The very first Net forum I joined (back in March 2003) was the ICC Discussion Forum on Delphi. I also used to participate in a couple cat lover fora on Delphi.
I rarely post on any of those church fora nowadays, since I completely lost interest. The only two fora where I'm currently active are SFI and MT.
All right, SwordLady and BobHubbard are Trek fans too! I love Star Trek Voyager (yep, I am one of the few that consider that my favorite of all of the Treks).
I post on 2 Trek boards, one Terry Brooks/Shannara board, a few parenting of twins boards, a few Sentai (Japanese Power Ranger) boards, and about a dozen martial arts boards.
I used to post on the pet forum on craigslist.org, but after a while the "self-moderation" got to be a bit too much - and the pet board was one of the tamer forums. I also read (and more rarely, post) on a couple of ITF-specific boards, but they are both down at the moment - one because it finally figured out it needs a live moderator (or 10) and the other for technical problems.
I don't believe it, there can't be, and even if there were I wouldn't post there, but since none exist outside of MT then I have nothing to worry about.
techexams.net and icertify.net, two IT certification boards. I used to read and post on more of them, but then I started MA training and found out about MA boards and it all went down hill from there.
I used to frequent http://coheedandcambria.com/board about as much as I frequent MT now-a-days. I still go there occasionally, I just don't post quite as much.
I don't really look around for forums to post on, otherwise I'd probably post on plenty.
www.homebrewtalk.com is about the only other one I frequent. I just picked up the hobby and it comes in handy. Just finished my first batch of beer, an irish stout. Tasted it after 3 weeks in the bottle and it was GOOOOOOD!