Groove

I'm compiling a list of the 20 most useful sites (non adult).

So far my list consists of:

Amazon.com http://www.amazon.com/
ESPN.com http://msn.espn.go.com/
Cnet http://www.cnet.com/
Download.com http://www.download.com/
eBay http://www.ebay.com/
Epinions http://www.epinions.com/
FirstGov http://www.firstgov.gov/
Google http://www.google.com/
Google Answers http://answers.google.com/
Information Please http://www.infoplease.com/
Internet Movie Database http://www.imdb.com/
iTools.com http://www.itools.com/
Lonely Planet http://www.lonelyplanet.com/
Mayo Clinic http://www.mayoclinic.com/
Microsoft http://www.microsoft.com/
Slashdot http://www.slashdot.org/
WebmasterWorld.com http://www.webmasterworld.com/
Yahoo http://www.yahoo.com/
Yahoo News http://dailynews.yahoo.com/
Yahooligans http://www.yahooligans.com/

Can you recommend any better candidates?