Moving Beyond OpenGL 1.1 for Windows
April, 2002 - Dave Astle
Excellent article on how to use OpenGL extensions. It also has a useful overview of what extensions are available.
The developer relations site of nVidia is full of good articles and demos with source code on 3D graphics.
OpenGL Programming Guide
The OpenGL Red Book, a complete guide to programming with OpenGL, version 1.1.
Batch, batch, batch: What does it really mean?
March, 2004 - Matthias Wloka
This presentation shows how batches are important in 3D rendering. It also shows how the ideal size of the batches changes with the speed of the GPU and CPU. A few ideas on how to improve batch sizes are given.
OpenGL Hardware Registry
Shows the OpenGL capabilities of a wide range of 3D accelerators.
Vertex Displacement Mapping using GLSL
Lot's of code samples for DirectX, OpenGL, and other things.
A site with lots of cool 3D samples with source code for both OpenGL and DirectX.
OpenGL Shading Language course
Oct, 2006 - Typhoon Labs