Here is a great metric conversion web site:
http://www.simetric.co.uk/si_water.htm
Find your weight on another planet!
http://www.exploratorium.edu/ronh/weight/
Difference between weight and mass:
http://www.newton.dep.anl.gov/askasci/gen01/gen01564.htm
The Periodic Table of Elements:
http://www.uky.edu/Projects/Chemcomics/
http://www.sciencenewsforkids.org/
http://www.martindalecenter.com/
http://www.scholastic.com/kids/homework/flashcards.htm