Mesa - An OpenGL-compliant Graphics Library.
BMRT - The Blue Moon Rendering Toolkit.
POV-Ray - The Persistence of Vision Raytracer.
The Mops - A 3D modelling package that uses BMRT.
Blender - Freeware modelling and rendering suite of tools.
Here are some links that don't really fit into any other category, yet are still worthwhile checking out if you are seriously considering using your Linux computer as a 3D modelling and rendering machine.
3D Software for Linux - Contains most (if not all) links in this document and then some.
3D Modelling Software for Linux - Links to software packages chiefly related to modelling.
3D Modelling and Rendering using Linux - A comprehensive site with articles and software that explains what this document summarizes.