I spent my whole prep period today playing with a site I hadn't seen before: PHYSICS 2000 @ http://www.colorado.edu/physics/2000/index.pl?Page=cover.html. I need to spend some more time there. I would love to know if someone has lessons that they are currently using that take students to the applets. I am especially interested in using the applets for the periodic table, electromagnetic radiation and half-life radioactivity. I will share anything I come up with.
Just an update as of 3/17. I tried to access the site, but it is no longer available. I reached out to CU Boulder and was told that Physics 2000 has been removed from their website because of old programs. There is no plan for upgrade. If you read Trish Loeblein's comment below, you will find that much of the work from Physics 2000 has been used to create sims on the PhET site. I was offered a CD with the program. They would still work on an older computer. If you are interested in getting one, you can contact the physics department at CU Boulder.