OpenGL Extension Registry:A record of OpenGL extensions, along with information about using OpenGL extensions and creating new OpenGL extensions
OpenGL.ORG:The official site for OpenGL information.
OpenGL ARB: OpenGL Architectural Review Board (ARB) consortium that governs OpenGL.
OpenGL Hardware Registry: A registry of all graphics cards and what OpenGL extensions they support.
SGI OpenGL Website: OpenGL information -- from the creators of OpenGL.