http://web.mit.edu/esgbio/www/
Developed by the Experimental Study Group at The Massachusetts Institute of Technology. Chemistry Review, Molecules, Cell Bio, Enzyme Bio, Photosynthesis, Mendelian Genetics, Central Dogma, Recombinant DNA, Immunology, and more.
http://pearl1.lanl.gov/periodic
From Los Alamos National Laboratory's Chemistry Division. Click on an element for History, Sources, Compounds, Uses, Forms, Isotopes, and more.
School For Champions
http://www.school-for-champions.com
A free e-Learning site on Physical Sciences, Mathematics, Biographies, Web Development, Education, and more...
http://froggy.lbl.gov/virtual/
You can interactively dissect a (digitized) frog named Fluffy, make movies, and play the Virtual Frog Builder Game.
Welcome to the Planets
http://pds.jpl.nasa.gov/planets
This is a collection of many of the best images from NASA's planetary exploration program. Just scroll to a picture of a planet that interests you, then click the image for planet profile, weather conditions, more photos, and other related information...