Not the common, digg, reddit etc, but the underground ones :P
Intelligent one hour long interviews with interesting people. Charlie Rose is a great interviewer, and actually lets people express their full opinion on a subject without cutting them off.
I don't know how he does it but he gets to interview all sorts of famous intellectuals, artists and business leaders. From Paul Krugman and Jeff Bezos to Michael Caine and Dennis hopper.
There are several new interviews every week and the back catalog will keep you entertained for months.
Everyone loves being really listened to.
That's interesting. Tell me why you think that is? ;)
http://bigthink.com for long, focused interviews with smart people
http://longform.org for good magazine pieces
http://www.kk.org/cooltools/the-best-magazi.php for phenomenally good magazine pieces
http://reason.com if you suspect yourself of having libertarian tendencies
I often find myself in need of an answer to the question: what are the most popular sites that have to do with x, y, and z? If you're looking for high quality websites about something, just type in a few keywords and have a go. Sorting by popularity (# times bookmarked on delicious) has turned out to incredibly useful, as it's highly correlated with quality. Also, I suggest that if you find any website that you like a lot you query it and see what comes up. Often times there'll be something even better... Or worse. (Did you know there are like 10 urbandictionary clones that all suck yet somehow manage to sustain themselves?)
To answer your original question:
wikipedia, urban dictionary, metafilter, news, pg essays, past and present Harper's indexes, tech/startup/entrepreneur blogs, TED and fora, and once inawhile popurls.
Articles, opinion pieces and discussion about science by top scientists. Often with a philosophical twist.
But in all seriousness, I find myself here a lot, along with:
http://mediaite.com/ <-- Good, video-heavy political coverage
http://reuters.com/ <-- News is good. And as wire services go, they're the most underrated.
Also a big fan of http://longform.org, which is ironic because of my own site's name.
http://apple.copydesk.org/ <-- Visual journalism blogger Charles Apple, who I read daily and who inspired me to do my own blog
http://www.theatlanticwire.com/ <-- An always-interesting aggregator of political opinion. The bloggers on The Atlantic proper, esp. Andrew Sullivan, I'm a huge fan of.
http://www.aldaily.com/ | for random goodness.
http://lifehacker.com | for me.
Disclaimer: This is my site. It's about as underground as it gets, considering only myself and a few of my friends use it. I stick things here that I find interesting, so you'll enjoy it if you have the same tastes as I do ;) Feel free to post anything you like as well, if you care to.
Long form essays that really aren't afraid to engage with an idea. Also, you should check out the personals section, as they are a lesson in wit.
And obviously http://www.nybooks.com/ , too.
Disclaimer, it is my project (http://news.ycombinator.com/item?id=1454934) but I'm trying to stock it with good stuff. Hope you browse.
I hope you fixed the code injection bug I had informed you of back then ;).
http://www.nytimes.com/timeswire/
I also swing by Kottke's blog:
drawar.com is also good for web design.