If you have a Generation III Prius (2010-present) with 15 inch wheels, you can pop off the UGLY wheel covers to release the alloy beasts underneath. Except - you'll have a hole in the center of the wheel that begs for a decorative cap. These are based on precise measurements of Toyota part #42603-52110.
This has a friendly atom, Hybridium, embossed in the top of the wheel cap.
Also fits Yaris, Vios
Note: the CAD file has changed since the photos were taken. The electron orbits now have a rounder aspect than the photo shows. I'm sure you will agree that this is an improvement to the design.
Nylon is NOT UV stable. For maximum longevity and downright good looks, you will want to paint this object. Acrylic paints with a glossy topcoat are a proven method of painting objects printed using Selective Laser Sintering.
Shapeways has a tutorial here: http://www.shapeways.com/tutorials/painting3dprintedsls
And a blog entry here: http://www.shapeways.com/blog/archives/129-painting-your-3d-printed-models.html
Further, you can locate the recommended Tamiya paints here: