There’s a bagpiping forum that I post on from time to time. I’m more of a lurker there, because I don’t have much to contribute. Some of the top competing pipers post or moderate there, so it’s more specific and esoteric than here.
I’m a regular on a board devoted to railroading, both large and small, called TrainOrders.com. Oddly enough, I’m also VunderBob there…
Yup, though not under this name. Used to post to some Might & Magic boards too, but they sank. Gave up on handbag.com (under the name of Diogenes!) some time ago.
As ever, a plug for NADS, which a few of us set up primarily for Irish and UK dopers (and anyone else who wants to join in - all welcome!) - which is chock full of incomprehensible slang, tales of drinking heavily, and Eurocentric cultural references.
and now for someone for whom the SDMB is more of an occasional thing 
ArsTechnica Best tech related board IMO, and where I am most active (not that means I"m very active there, either)
Fark Everyone needs to shut their brain off sometimes
I frequent both the NaNoWriMo and NaNoEdMo boards, and lurk a little on Forward Motion, all of which are boards for writers.
Winamp has a mesasge board I’ve posted in a couple of times. They even have a Bitchlist which is similar to our Pit. And I post regularly on a couple of metaphysical boards the average Doper would ridicule me for. :rolleyes:
Bad Astronomy has a message board? I’m definitely gonna check that out!
My main internet haunt is bladeforums.com. I’m registered on a whole bunch of other knife and gear related boards, but spend more time at BF than anywhere else.
I stop in at customerssuck.com just about daily (Ok, daily). What can I say? There’s a bunch of cool people there.
I’m a part of a couple of bands’ message boards, but in the end, nothing compares to the 'Dope.
Like jjimm, i’m now a regular poster on NADS, under the same name here. just about everyone there can be found here, albeit some under different handles.
I look at a Ring EZboard forum, but dont really post there. I think i’m still registered at the Red Meat Conference as well, but I haven’t looked at that in a long while.
I lurk at a few boards. I was a regular at spacebattles but gave that up. I post occasionly at sd.net, and have lurked for years at the ttlg forum. I also frequent the KA forums for new mods and the like.
Banquet Bear mentioned this forum once and I wander in now and again. I would stay and post more bu the board is slow to load for me.
I only belong to this message board.
Several others, but I’m not as active on them as I am here.
A few art-related boards, a Stargate board (yes, geeky), a few Macintosh computer boards (more geekiness), and, uh—I think that’s it.
Yeah, that’s it.
I’ve found several other citizens of the Fortean Times message board in here. I’m also a member of planetjitsu as well
I admin some ezboards. One I co-founded with 50 posts per day or so, one with over 100 posts per day (both Star Wars roleplaying). I also admin one for General Discussion (entertainment to politics to religion, 100/day), and a smaller one (medieval/scifi roleplaying) with around 20/day.
I am also a regular on a Stargate message board, and a lurker on Fark and JREF.
Ghastly! Funny to see his website pop up here. He’s a regular poster on the Soapbox at www.wilwheaton.net. I’ve been posting there for over two years, along with the Snopes ULMB and occasionally Fark. I also indulge my sister by playing an RPG over at roleplay.darkmark.com.
Yeah, I stay busy 
Besides SDMB, I post at four different Pokémon boards. And a couple of Draw BBSes too.
I used to hang out at several Buffy/Angel message boards. Now I am pretty much here and on the Buffy Naughty Board, but not under this name.
I post on my school’s message boards, which are fun because I know everyone and it’s really active.