Brdf map

BRDF stands for Bidirectional Radiance Distribution Function, a way for describing how a surface reflects light. In game shaders BRDF is usually a rougher approximation, simplified for faster rendering. A BRDF map is a vertical gradient mixed with a horizontal gradient, each controlling how the surface reflects light relative to a different angle: one for the camera, and the other for the main light.

BRDF Shaders
1. Brice Vandemoortele and Cedric Caillaud's BRDF shader for Maya supports a BRDF map. It's also been [ported to 3ds Max by Christoph Kubisch aka CrazyButcher. More info in the Polycount thread Free Maya/max cgfx/fx Shader. Update: New version here with many updates, including object-space normal maps, relief mapping, self-shadowing, etc.

2. Kostas Gialitakis' Maya CG shader also supports a BRDF map. More info in the Polycount thread "KoddeShader", a Maya CGFX shader.

3. Laurens Corijn's 3ds Max viewport shader supports several lighting techniques that are similar to BRDF.