Fractals with Canvas3D
If you have the beta of Firefox 3 and feel like watching some hypnotic fractals, I recently made a demo using the Canvas 3D preview. It's done using an OpenGL 2.0 fragment shader, so the precision isn't amazing - there's only so much you can do with 32-bit floating point numbers... But it's not too bad if you can't zoom in.
See it here (note - it doesn't work at the moment). It requires the canvas 3d extension to be enabled, and OpenGL 2.0 support.