OpenGL

Apple's OpenGL Resource
Developers tools and documentation for using OpenGL on Apple systems. Includes a list of OpenGL extensions supported by Apple, how OpenGL fits in their architectures, and performance tips.
http://developer.apple.com/graphicsimaging/opengl/

NVIDIA Developer Zone: OpenGL
OpenGL related software, tools and documentation for developers.
http://developer.nvidia.com/page/opengl.html

OpenGL Architecture Review Board (ARB)
Consortium that governs OpenGL.
http://www.opengl.org/about/arb/

SGI OpenGL Website
OpenGL information from the creators of OpenGL.
http://www.sgi.com/products/software/opengl/

Wikipedia: OpenGL
Comprehensive overview of OpenGL, including history, pipeline architecture, language bindings and sample code.
http://en.wikipedia.org/wiki/Opengl