Library of math and science java applets. These let you set your own variables and conduct online lab / experimentations. Subject areas include bio, chem, physics, earth and space, and math.
Contains math and science simulations for all major science disciplines (earth science, chemistry, physics and biology), and math tools and applications.
This has "science interactives", or virutal manipulatives that students can use. I've seen the roller coaster before, but I haven't seen the rest. Their new interactives include DNA, Periodic Table, Dynamic Earth, and the Rock Cycle.