http://school.discovery.com/  -Great resources for students, parents and eachers.  The Best part of this site is the puzzle maker.  It lets you make a variety of puzzles where you type the info, and the computer scrambles it and makes it usable and easy.
http://puzzlemaker.school.discovery.com/  - The puzzlemaker part of the site.
http://www.coolmath.com/
http://www.kidsclick.org/
http://www.ajkids.com/