If you're of a rationalist / philosophical bent you might like http://lesswrong.com
"Less Wrong is a community blog devoted to refining the art of human rationality."
I'm surprised that nobody has mentioned /. yet.
Chips&Dips, er Slashdot, was the original high-quality tech forum on the internet. In recent years it has gone to trash, but it is still the model community-driven tech news forum and occasionally has very good commentary.
Investing advice inspired by Jack Bogle: https://www.bogleheads.org
These Hacker News clones seem like good candidates for decent communities:
For beer: https://www.beeradvocate.com/community/
That links to the forums where you see some good discussion. Also the reviews of beer on the site are quite extensive.
https://feedit.agfunder.com/ for agriculture and food related technology and investment.
Full disclosure: this is a project I'm working on, and comment functionality is coming.
Nonforum.com is for sustainable / resilient agriculture+composting+earthships, alternative lifestyles, personal experiences, and forward-minded things that would otherwise not really have a home on the 'net.
There's a small write-up of things we are trying to foster at https://nonforum.com/about.html (or just click on the (non) logo card on the front page)
Still pretty nascent, and I haven't submitted a show HN yet because there's no commenting functionality up yet. On the bright side, nonforum functions as a nice link-sharing platform, and votes and submissions show up in real-time (no page refresh required).
Currently in semi-open beta (one needs an account to submit new links/write-ups and to vote on things), you can request an invite code by providing your e-mail, or, at the moment just asking me to send you one.
Indie Hackers (https://www.indiehackers.com/) in my opinion is an up and coming badass community.
Not much content on there, but the content thats there is nothing I have seen anywhere else
slatestarcodex has a great community following it and good moderation.
One I frequent is https://hashnode.com
It's still not very big but seems to be growing. And it's completely bereft of political talk, which I find refreshing.
MetaFilter still kicks ass.
There's https://lobste.rs/ it's invite-only to comment, but not hard to get.
I wonder if there are similar sites but more bootstrappers oriented (rather than investors' pocket burners).
I've had a very conflicted experience with SomethingAwful in the past. Parts of it feel like a quality and tight community, others are just endless shitposts. They might have severely dipped in activity as well over the past few years.
I've built several fb groups I built from the ground up, but cap membership at 200 members.
Still want to build out cronofy.com integration to help members connect/meetup in person.
For (online)poker there's forumserver.twoplustwo.com
http://designernews.co for well, Designer News.
This site isn't only focused on tech, there's also a lot of tech entrepreneurship - particularly the VC-funded Bay Area variety, and also a bit of gossip about that community.
For tech, https://lobste.rs is decent. There's more interest in papers and proofs-of-concept than here. (Give a link to your profile on Twitter/GitHub/here in #lobsters on Freenode and someone will give an invite pretty quickly.)
For bootstrapped entrepreneurship, https://barnacl.es (my site) is small but welcoming and growing. (No invite needed.)
Reddit. For instance, the programming subreddit.
My favorite is Lobsters: lobste.rs
metafilter.com is a good general/link-aggregatey site. It's got a strong "SJW" contingent though, so take that into account.
If you really want to have your perspective challenged many times and want a community that values truth and only raw truth over hurt feelings or political correctness go to https://boards.4chan.org/pol/catalog
Remember it has absolute free speech (anything legal in US)
Just suspend the initial disgust and read the comments, you'll surprisingly find very deep commentary and raw truth morsels of this indifferent universe. Like coffee it's an acquired taste.
Parts of reddit are good. They're probably the closest thing you'll find to HN though many here would have to admit it.