Updated as I feel like it

Google for everything
Slashdot for news and events
Wikipedia for an overview of any subject
w3schools for learning about the web
Physics Forums for learning and helping with math and science (I no longer go to this site but I used to be a "science helper" there and I can vouch for the helpfulness of the regulars)
Python, Haskell, and Java documentation
The Onion for informed geopolitical commentary
Newgrounds for games
Youtube for music videos
Something Awful for the "photoshop Fridays"
The Cat programming language, which is a small stack-based language which is interesting because it includes static types
An interesting article about data and codata ----12-08-2008----
Pournelle's Iron Law of Bureaucracy----12-19-2008----
Principle of Maximum Entropy----12-20-2008----
CWE/SANS top 25 most dangerous programming errors----01-12-2009----
Broken Window Fallacy----02-16-2009----
Fizzing neck noise----02-20-2009----
Practical Psychology----03-06-2009----
Fun Japanese Game Show----03-16-2009----
A very informative breakdown of the ways the meanings of words tend to change ----03-29-2009----
Lambda the Ultimate, the programming languages weblog ----05-31-2009----

Webcomics

xkcd, Basic Instructions, Looking for Group, Dinosaur Comic, Dilbert, Married to the Sea, Nukees, 8-Bit Theatre, Toothpaste for Dinner, Goblins Comic, Boxjam's Doodle, Saturday Morning Breakfast Cereal,Order of the Stick