If you’re interested in Astronomy, check out Bad Astronomy. There’s a link to the message board on that page. The site is run by Phil Plait who posts here at SDMB as The Bad Astonomer.
If you have more time than it takes to read the current threads (I wish I did) go back and read some of the past threads. JDT alone will keep you busy for weeks.
I will toss out a couple of decent special purpose boards.Slashdot is pretty good for technology or geek related issues, if very anti-Microsoft. Another board you’ll see a few Dopers at is The Pizza Parlor if you’re interested in discussing Christianity specifically. Our own Polycarp is a moderator there, and it’s where I go if I have church related questions. The only remotely comparable group I know of on-line in terms of wit and variety is the Hell’s Mensans Group on Yahoo, but that is a private, Yahoo Group, which means no separating of posts into individual threads. The conversation is good, but following individual conversations gets difficult for me.
This is the only message board I go to regularly (too regularly!) because the conversations here are not only better than most message boards, they’re better than a fair number of real-life conversations. It’s also a place where you can discuss topics which can quickly lead to flared tempers such as religion and sexuality without getting into a flame-war. You can also learn things you never dared to ask or never knew existed. Sometimes I might have been better off keeping it that way, but fighting ignorance includes my own.
Congratulations, my friend, you’ve found nirvana. Just be warned – a former poster called this place “cyber-crack” and I’ll second him.
CJ
Oh yeah, I can see it now…
“So dreamer, what do you do in your spare time?”
“Oh, I do an enormous amount of cyber-crack, you should really try it sometime!” 
If they’re like you, keep pushing the stuff! 
Besides, I’m working on getting another friend hooked (as if agentfroot weren’t enough).
CJ
This is such a singularly unique place on the web, sort of like **Cheers ** **MTV Spring Break ** **Fraiser **and **Who Wants To Be A Millionaire/Jackass/Survivor ** .
I’ve only just found, and am lurking there, http://www.forteantimes.com/forum/forumdisplay.php?s=&forumid=11]This Which is Fortean Times Message board, same Vbulletin as ours and faster too. Caters to news of the strange/phenomena and the MPSIMS that we carry on so about. They seem to like de-bunking stuff too. It’s based in England so some of the slang is over my yank head.
:smack:
How about a third try, Shirley? 
To rsa, cjhoworth, and Shirley Ujest: Thank you for the links I glanced over them already they look good so far I will be sure to check them out in detail as soon as possible.
To Tinkertoy: Yes, I will be sure to go back and do so; the sheer volume of information on Straight Dope and school is the only thing keeping me from doing it immediately.
To 5-HT, red_dragon60, iampunha, Cougarfang, masonite, dreamer, cjhoworth, and neutron star: Thank you all for you opinions, comments, and help.
To Lynn Bodoni: Thanks for moving this thread. What is a hamster? (Besides the obvious little fir-ball in the cage.)
Benjamin of the darkbrigade
You want other message boards? My word, you must have too much free time, or not enough dedicatiopn to the Dope yet!
Seriously, this one is the best. I do post at a few other ones, but they’re much more topic-specific. Unless you’re interested in bridal stuff or historical clothes, they’re pretty boring…
kniz, I couldn’t get my ass kissed in here if I tried…
Seriously, I’ve found other special-interest boards (hardwarecentral.com for instance), but nothing quite like this.
I heard a rumor somewhere that another board, VERY much like the Dope could be found at Metatus.com
I haven’t checked it out in awhile so, who knows?
Lady Ice
Good grief! I was more disturbed than I would have ever guessed. Am I hooked or what? It is great to be back. I am relieved.
This is the best multi-purpose board.
t-keela, metaus is ok, but doesn’t change all that much. I got bored with it really, really fast.
Stick around… we have cool smilies (although I never use them, it’s cool to know that I can)
Oh yeah… and the people… they’re cool. 
(ooh! I used one!)
If you’re into sports, Fanhome.com is good. That’s how I found out about this board.
After lurking awhile on the SDMB, I abanoned my old message board (which shall remain nameless) in favor of this one. The near-realtime interaction is great, as are the variety of topics, and the cool people - quite a few of whom I’ve met IRL. It’s a wacky community, but one I’m glad to be a part of. Just knowing I could be stranded somewhere, and a Doper would help me out, and/or take me in, is an example of how incredible we all are.
Just hang out here for a while. You’ll want for nothing more.
Try Fathom for the next-closest thing to the SDMB.