XGen cubes rendered with Arnold
Another gorgeous fractal / generate art experiment created by Lee Griggs using XGen cubes rendered with Arnold. He uses a texture map to drive the length and color of an XGen primitive. While I haven’t personally used Arnold yet, it is claimed to be able to render millions of instances of geometry without any problems.
Lee has a ton of other stunning CG experiments mostly created with Arnold so be sure to take a look through the rest of his site.