Association of Science Education
http://www.scienceonestop.com

Science Resources
http://scorescience.humboldt.k12.ca.us
(from California)

Physics 2000
http://www.colorado.edu/physics/2000/index.pl
interactive

Virtual Labs and Simulations
http://www.hazelwood.k12.mo.us/~grichert/sciweb/applets.html
interactive