I just learned that you can get something like this: Source: Shapeways custom-made on the internet. 3D printing in sterling silver and even 14K gold This polished silver Buckminster Fullerene is AU$126 here. They're small (4cm), but wow! Many more to choose from. What's your favourite?
Freakin' sweet knots does some good ones http://freakinsweetapps.com/product-category/rings/ Source: http://freakinsweetapps.com/product/thick-woven-ring/# If you like 3D printed knotwork