Here are a few I enjoy checking a few times a month or so.
The Straight Dope - A trivia/obscure knowlege column that appears in the Chicago Reader -
http://www.straightdope.com/index.html
Getting Things Done Forum at David Allen Company - GTD is my favorite personal time-management system -
http://www.davidco.com/forum/forumdisplay.php?f=5
How Stuff Works - Lots of cool articles about science and other interesting stuff. Recently the site has started to feel too commercial to me, but the archived articles are still great.
www.HowStuffWorks.com