The Altgeld Math Models. Below you will find around 170 of the models that were photographed in March 2005 when the third floor model cases had to be emptied and moved. The models were carefully moved into the undergraduate lounge and arranged in a miniature "model museum" for two weeks, where each was carefully photographed and is now available for your enjoyment below. [more inside]
Flash Java Fun - 'Building Houses With Side Views' Entertaining Java game/exercise/doodad. [more inside]
Here are some beautifully rendered views of polytopes, and a few more. The rendering program, Jenn 3D, is free and downloadable, (OS X, Linux, Win) and includes some really dazzling fly-about and camera effects as well as tons of high-dimensional models to explore. There's also a mind-boggling possibility of playing Go on boards in projective space. Via the Math Paint blog, which leads to other interesting places...
You have spacial skills. Apply them in Building Houses 2, on mathsnet.net. Or freestyle in Building Houses 1. Or at night! Oh and also there's like a hundred more puzzles over there too. Some java required.
Minimal surfaces in 3D (red/green, or stereo pairs), with rotate and zoom. If you want to go beyond the eye-candy aspect, here's the obligatory Mathworld link, the classic intuitive explanation, and a raft of additional information. If you like eye-candy, don't miss the ray-traced minimal surfaces and these interesting, but non-minimal surfaces.