NeHe OpenGL Tutorials
A great set of varied tutorials on OpenGL topics. Includes full source code and descriptions.

OpenGL 2.0 Specification
The official documentation for OpenGL 2.0.

OpenGL Shading Language Specification
The official documentation for the OpenGL Shading Language (GLslang).

glBegin(), glEnd()
Quick reference for these very important OpenGL functions.

OpenGL Extension Viewer
Very handy tools for exploring OpenGL compatibility on a computer. Shows supported extensions and functions based on graphics driver.

Transformations
A very good reference on one of the most important fundamentals of OpenGL.

OpenGL Matrices
Information from U of Iowa about OpenGL matricies.

GLUT Function Reference
Quick reference for the GLUT library.

GLUT for Win32
A version of the GLUT library compiled for use on the Microsoft Windows platform.

GLUT for Linux
Original GLUT library for X Windows on Linux.

FreeGlut
An implementation of the GLUT library with some improvements over the original.

Other Toolkits
Alternative windowing toolkits if GLUT is not an option on your platform.

FreeImage Library
Handles PNG, TIFF, GIF, JPEG, TGA, BMP, etc. Easy to use with OpenGL.

lib3ds Library
Works with all aspects of a 3DS file.

Blender
Great free modeling and rendering software written using OpenGL.

Milkshape 3D
Good modeling software for beginners.

3D Studio MAX
Widely used in the modeling field, not free.

Maya
Another industry mainstay, also not free.

XSI
Another industry mainstay, also not free. This is the software for character design.

NVidia HOWTO
Instructions for setting up an NVidia card under Linux.

ATI Radeon HOWTO
Instructions for setting up an ATI card under Linux.

Visual C++ 2005 Express
A very cost effective Microsoft development environment. If you can find Visual Studio 6.0 you should use it instead since I haven't figured out how to avoid linking .Net stuff for distribution.

Microsoft Platform SDK
Windows Server 2003 platform sdk (for 2000 and XP also). Contains OpenGL and Win32 library stuff that is necessary for OpenGL programming.

Notepad++
A great programmers editor. Even has some support for auto-completion. Please let me know of other alternatives to Visual Studio that you use.

OpenGL Developer Site
Information straight from the horses mouth as it were.

Xcode Site
Information on Xcode Development IDE.

Xcode Setup
How to create an OpenGL enabled project in Xcode.