I recently got myself an invite to <a href="http://lobste.rs" rel="nofollow">http://lobste.rs</a>. It's a <i>lot</i> less active than HN, but part of that is no doubt because it's invite only.<p>The big thing for me (and I suspect others given the recent discussions about it here on HN) is that the voting system is much more transparent and specifically aims to solve the issues found on several other sites with voting, i.e.: down votes require a <i>reason</i><p>As my inviter did for me, I'll happily invite active HN members who'd like to join lobste.rs
I used to love Quora, but lately I've found it really hard to enjoy. There's a lot of crappy content. I heard they're trying to change this somehow, I'll wait to see.<p>There are some subreddits that are pretty great: /r/askhistorians, /r/credibledefence and /r/neutralpolitics are all pretty good.<p>LessWrong.com has some good reads, and so does ribbonfarm.com.