I used to be a regular on the Salon Table Talk board “Mothers Who Think” and while it certainly doesn’t offer up the variety of the SDMB, there are - or at least used to be - plenty of decent folks over there. It is a pricey subscription, though, I think.
I love the snark on Fametracker. It’s very specialized, of course, but the grammar is top notch.
The Fark forums are certainly not where I’d turn for an intellectual discussion, though. I mean, just read the presidential debate threads…
I haven’t found any boards quite like this, but I think that as a general rule the best boards are on the sites with the best content outside the board. This makes sense to me, because the better the content is on a site, the more people it will attract. So the best board for Star Wars fans would be on a site with tons of unique Star Wars info, and the best board for people who love to garden would be on a site with tons of great gardening info. So it’s not too surprising that the best board for talking about every random thing under the sun is on a site that holds the answers to just about every random question there is.
You must be a red stater.
www.b3ta.com
Has no censorship.Anyone can post anything.For those who really wish to venture into the dark depths of the human soul 
I used to love posting on b3ta, but these days it just seems to be taken over by 14 year olds who think they’re webdesigners or potatoshop experts.
Has anyone asked the Dope to start up a parenting section? Might be enough parental dopers to form a nucleus and get things going.
NewsNet, the mother of all message boards.
I would have to nominate the board at JREF (JREF ). It has lots of intelligent conversation and critical thinking.
There are five general interest message boards, commonly seen as unofficial spinoffs of the SDMB, that were created and managed by other Dopers; Fabulous Forums of Fathom, Unaboard, G’Dope, NADS and Skip’s Magic Board. These sites are closely connected to the SDMB community, but not under the purview of the Chicago Reader. These sites, especially FFF and Unaboard, often serve as a “refuge” during times when the SDMB is down for a prolonged period.
There are also Doper-run boards that are more niche-oriented, and usually not lumped in with the spinoffs; Bad Astronomy Bulletin Board (astronomy and astrophysics myths and facts), Cyburbia Forums (urban and town planning), NoClueBoy’s Star Trek Discussions (ST, of course), and probably others that I don’t know of. Lots of Dopers belong to BA and NoClueBoy’s board; there only a few on Cyburbia. Again, these aren’t formally associated with the Straight Dope and the Chicago Reader; they’re just run by Dopers.
Something Awful – NOT run by a Doper, unless the owner, Lowtax, has a membership here that I don’t know of – has some SDMB-like traits. The demographics are much different, though, skewing heavily towards twentysomething males. It’s pay-to-post, and additional features (archives, searching, etc) cost extra.