George Hart has a bunch of amazing rapid prototyping geometric structures at http://www.georgehart.com/rp/rp.html
These are the parts to make Face-centered Cubic Voroni Tetrahedron of various sizes.
The pieces here have been scaled 7x and oriented to print nicely on a makerbot/reprap. For the originals, and other pieces to allow making octahedrons, see George's original page at http://www.georgehart.com/rp/FCC.html
The pointy bits on these are susceptible to blobbing, so it is best to take preventative measures, such as using skeinforge multiply to print a few at once, or potentially using the cool plugin (I took the former approach).