http://www.billnye.com/ -- Everyone's favourite scientist has his own page! This site has everything you want to know about Bill, plus awesome demo activities that you can do at home!
http://www.chem4kids.com/ -- Remember how much fun we had with our chemistry unit? (Don't give me that face -- you know you had fun!) Well, if you ever find yourself forgetting what we covered, this is a great site to review! It has everything you need to know about matter, elements, and atoms. It even has the periodic table for you!
http://www.braingle.com/Science.html -- If you're looking for something fun to try, or want to sharpen your mind, try some brain teasers! These are special Science brain teasers for you to do... if you feel brave enough to try the challenges.