Youtube - as bad as certain aspects of YT are (eg, comments), there is a TON of great educational content on there, as well as music videos.
Reddit: Yes, the default subs are horrible, but there are a lot of great specialized subs as well.
Coursera: taking a couple of classes now
Facebook - not happy to admit this, but it's force of habit. :-(
news.google.com - news
arxiv.org/corr/home - CS papers
wral.com/weather - local weather
amazon.com - I'm on there either ordering books, adding stuff to my wishlist, or just looking up a book I might want to buy "one day", or checking on the status of an order, pretty much every day.
dilbert.com - lulz
phins.com/phins-urls.html - Dolphins news
digg.com/reader - feedz