3Delight
Renderman compliant renderer. Excellent quality, and the first license is free! Now comes with a plugin for Maya.

Air
Free Renderman compliant renderer.

Fundza
Reference and tutorials about the Renderman protocol

Liquid
A free RIB export plugin for Maya.

Shaderman
A free utility that helps you create renderman compliant shaders.

RenderMan Academy
A great didactic site about renderman.

RenderMan Repository
This RenderMan ressource site contains a lot of shader examples. You can find the SIGGRAPH publications on Renderman here.

Pixar
The company that develops the Renderman protocol.
RiSpec can be found here.

Pixie
Open-source renderman compliant renderer.

Renderman google group
The comp.graphics.rendering.renderman google group.

Alex Dragutescu

Andreas Bauer

Bruno Lessieur

Caroline Thoumire

Cinzia Pegorin

Daniel Evans

Jean-David Solon

Jean-Renaud Gauthier

Jeff Newton

Jorge Pimentel

Federico Ghirardini

Harry Bardak

Manfred Kramer

Mark Osborne

Mathieu Burri

Studio Inverse

Xavier Bernasconi