Jakob Nielsen's Website
http://www.useit.com/

National Cancer Institute's Research Based Usability Web site
http://www.usability.gov/

Human Factors International
http://www.humanfactors.com/home/default.asp

For Use.com: The Web site for usability and design
http://www.foruse.com/Resources.htm

WebWord Usability Weblog (delivered by email every day) (visit the archive)
http://www.webword.com/

UI design.net: The Webzine for interactive designers
http://www.uidesign.net/

Webzine: User Interface Engineering
http://world.std.com/~uieweb/