Interactive physics demonstrations/explorations on the web:

Physics 2000, U. Colorado Introductory Java windows and tutorials for EM charges, atoms, quantum mechanics, waves/particles and more!

Fourier analysis, Gustavus Adolphus College A simple Java demonstration of wave superposition.

The Web Physics Project, Davidson College Java applets demonstrating a wealth of physics principles (optics, EM waves, and more)!

The Virtual Laboratory, University of Oregon Java applets demonstrating a wealth of physics and astronomy principles!

Virtual Physics Laboratory, NTNU  Additonal Java applets demonstrating a wealth of physics principles!

Gamelan Interactive Physics  Additonal Java applets

Java Applets on Physics  Additonal Java applets

Roman Pfaff's ExploreScience   Shockwave based demonstrations

Fowler's Physics Applets   More java applets