Relativity Visualized (http://www.appliedthought.com/InsightPress/RelativityVisualized.html)
Some fun links:
http://www.adamtoons.de/physics/relativity.swf
http://www.spacetimetravel.org/tuebingen/tue0.html
http://www.adamtoons.de/physics/gravitation.swf (needs Flash)
http://www.adamtoons.de/physics/relativity.swf
http://www.youtube.com/watch?v=VSRIyDfo_mY&mode=related&search=
http://www.anu.edu.au/Physics/Savage/TEE/site/