Pixar - the company that have developed RenderMan specification.
Blender - great open source package for 3d modelling, animation, rendering, and postproduction.
K-3D - complete program for modelling and animation.
Pixie - an open source photorealistic RenderMan renderer with many advanced features. This is a renderer we mostly use.
Aqsis - an open source high quality, photorealistic, 3D rendering solution.
RenderMan Academy - good resource for beginners and experts.
RenderMan.Org - many documents about RenderMan.