Here are few websites I would like to share. Some are geared towards children but I found them all to be very helpful.

Chess Kids
http://www.chesskids.com

Chess Guru
http://www.chessguru.net

United States Chess Federation
http://main.uschess.org/content/view/7324/28/

Chess Dryad
http://www.chessdryad.com/education/magictheater/

Chess.com Play. Learn. Share.
http://www.chess.com