This website has outstanding interactive demonstrations and simulations for physical science.  Check it out!

http://phet.colorado.edu/new/index.php

Contains various dynamic demonstrations.

www.explorelearning.com

Very nice, user-friendly website with content from all academic areas, including science and technology.  Check out the videos that accompany the content.

www.brainpop.com

This is a cool chemistry website that shows how Mendeleev arranged the elements, contains activities, and provides downloadable material.

http://www.chem4kids.com/

I recommend this site for asking questions and getting information about fusion, matter, energy, magnetism, or electricity.

http://ippex.pppl.gov/interactive/

This is a great website to visit if you are looking for a cool experiment.  It also lets you figure out the science of how skateboarding tricks work!

http://www.exploratorium.edu

This is a great all-around website that provides an explanation about most everything.

www.howstuffworks.com

This website has a terrific interactive Periodic Table of Elements, games, puzzles, a student zone, and information on new discoveries.

http://education.jlab.org

Visit http://apps.exploratorium.edu/10cool/index.php?cmd=browse&category=12 for websites on numerous topics ranging from histology to bugs to virtual knee surgery.