Check out the contest on http://xbox360homebrew.com/

Here are some more!

http://www.thezbuffer.com/

http://learnxna.com/default.aspx

http://xnaspot.com/

http://exdream.no-ip.info/blog/

http://www.ziggyware.com/

http://www.xnadevelopment.com

http://www.xnatutorial.com/

http://www.sharpgames.net (Brazil/Portugese)

http://www.thehazymind.com/XNAEngine.htm

http://pilot.vector4.com/xnainfo/

http://xna.animered.net/ (Spanish website)

http://rasmithuk.org.uk/