http://www.walter-fendt.de/ph14e/ Java Applets for Physics. Check out this website at www.walter-fendt.de/ph14e/ Walter Fendt's site contains a plethora of physics applets, explaining a wide range of concepts. My favourites to use in teaching are: Elastic and Inelastic Collision; Forced Oscillations (Resonance); and Standing Wave. I also just spent some time watching the speeds of the planets as they orbit the Sun, in the Kepler's Second Law applet. The great thing about them is that you, (or students), can change parameters and see what happens.
You will require Java to be installed to watch the applets. However, most computers will have this already installed. Those that don't, there is a link to were you can download it.