Jean-François Colonna makes elaborate and striking mathematical images. I only wish they had more annotation.
The Virtual Terrain Project collects links about the state of the art in realtime simulated environments, from “why can’t you make better trees?” to “how do you decide when part of the field of view can be rendered more sloppily?”.
Harpsichord made almost entirely of Lego parts. (vectored by Sam Yorko and Clint Chaplin)
A Webwide World by Ken Perlin, NYU, 1998 – Java applet that rapidly generates a fractal planet. Unlike the Planet of the Day generated by ppmforge, Perlin’s planet is three-dimensional and can be rotated.
Matthias Wandel’s insane constructions (link from AlterSlash). From the same site: some surprisingly effective mathematical drawings.