Some of my favorites...

Video Games

seriousgames.org - An initiative for application of games in business training, education, public policy, and healthcare.

gamefly.com - Rent commercial video games. Why pay $60 a game when this is available?

unity3d.com - An up and coming game development tool described as "the Final Cut Pro of game authoring tools", this tool already exports games to Windows, Mac, the Wii console, and browsers.

atmosphir.com - A cool video game level making tool. It's free, and for Mac and PC.

civworld.gameslearningsociety.org - A site hosted by the Games +Learning + Society group at UW Madison, with specialized educational content for Sid Meier's Civilization III. This content is aimed for use by teachers and parents to use Civilization III to play out realistic historical simulations.

Entertainment

slacker.com - Slacker Radio has some excellent online music stations. I stream their Alternative station, and it seems to adapt to the kind of stuff I enjoy. They've got Blackberry and iPhone apps too.

Techie Stuff

tomshardware.com - Great reviews on the latest and greatest computer hardware (motherboards, CPUs, video cards, etc.).

speedtest.net - Find out how fast (or slow) your Internet connection really is.

steves-digicams.com - Professional reviews and news on the latest digital cameras.