Smith Chart, courtesy http://www.sss-mag.com

Demo version of a executable Smith Chart file (cool!) by Fritz Dellsperger, who has other interesting stuff at his website.

Great Java animations from Agilent Technologies that "add life to vectors and help the student visualize how time-varying signals combine to make a waveform."

Animated videos of how waves propagate.

An electric pickle.

Animated videos of how acoustic waves propagate and reflect from different types of boundaries.  These help you to think about why reflections do what they do.  The reflection from the hard boundary is like an electromagnetic short, and the reflection from the soft boundary is like the electromagnetic open.

More animations that show concepts related to the superposition of waves.  Of particular interest is the demonstration of how a standing wave can be created from two traveling waves.

DC and AC Motor Animations