ARB

• ARB Fragment Program Specification - The OpenGL low-level fragment shader language specification. Includes detailed documentation on APIs and assembly instructions.
• ARB Vertex Program Specification - The OpenGL low-level vertex shader language specification. Includes detailed documentation on APIs and assembly instructions.
• ATI Fragment Program Info - AMD/ATI's OpenGL SDK; includes information on ARB Fragment Program support.
• Basic Vertex Shader - A clean example of a no-frills vertex shader. demonstrates input/output semantics, application variables and state values.
• Fragment Programs-ATI R3xx vs NVidia NV34 - Examines differences in fragment shader behaviors between ATI and nVidia cards. Includes code examples, and operations to avoid for improved portability.
• Low Level Shaders - A rare collection of ARB sample code.
• OpenGL ARB Vertex Program - Cass Everitt's presentation on GL_ARB_vertex_program. Overiew of OpenGL shader pipeline, vertex attributes, registers, constants, variable types, input/output semantics, list of ARB instructions and example ARB code [PDF]
• Shader Designer - Vertex Shader Example - An example of ARB vertex shader code generated by Shader Designer. Includes a screen shot of a metalic shader.