An intro to modern OpenGL
— Paul Annesley, May 2010
An excellent OpenGL tutorial; beware other documentation and tutorials which endorse deprecated APIs and practices.
Modern enough to be applicable to OpenGL ES 2.0 (and therefore WebGL), which requires vertex and fragment shaders to be written in OpenGL Shader Language to take advantage of the programmable rendering pipeline, and which removes much of the procedural (glBegin/glEnd) API.
Adapting this tutorial to Cocoa Touch for iPhone/iPad OpenGL ES 2.0 development was relatively easy, and beat any iPhone OS specific documentation for ES 2.0 that I’ve found.