Funny, I have spent years trying to escape the small town/small-minded feel of most online communities. I favor larger sites these days, where there is somewhat less entrapment or entrenchment due to personal politicking.

That being said, I currently spend more time on MetaFilter than on HN. I sometimes don't show up here for months at a time. As an openly female member, I have found this boys club in many ways less than welcoming. Possibly not a good thing to admit.

Ruby Rogues Parley - a paid email list (that is now a Discourse forum) around the Ruby Rogues podcast.

It's basically a private forum for technical topics in Ruby. Pretty high signal-to-noise ratio.

Obviously Slashdot. It isn't quite as huge as it once was, but it's still thriving and has some great headlines (though the quality of comments has been stuck in Eternal September for a while now).

Then again if you're looking for message boards, I don't really participate in any, so I can't help you there.

Slashdot still generates some great discussion and has quite a few smart people participating. The moderation system is brilliant and keeps the perceived signal-to-noise ratio of the comments high, even if there are a lot of pointless comments (they're just made effectively invisible).

I still worry what Dice will do to the site when they inevitably get around to redesigning the desktop interface. The new mobile interface is IMHO much less functional than the old one.

At a risk of stating the obvious... StackOverflow/StackExchange. Not a forum per se, but definitely a community. :-)

I mean in the more traditional forum sense. That layout still doesn't make me feel like I know anybody, and it's missing the crapshoot banter/offtopic forums.