The tutorials section includes a variety of contributions aimed at making OpenGL easy to learn by explanation and example.
CodeColony has posted a number of interesting tutorials in the SDK and has many more back at their web site. These tutorials range from your first triangle to much more advanced techniques.
Lighthouse 3D offers direct links to their tutorials covering the spectrum from GLUT to GLSL, computer graphics math to stencil shadows.
OpenGL Samples Pack is a collection of OpenGL samples based on the OpenGL "core profile" specifications. The project aims to promote the new OpenGL features making easier version transitions for OpenGL programmers with a complementary documentation for the OpenGL specification.
TyphoonLabs GLSL Course will show the student all about GLSL shaders, from the language specs to advanced shader techniques, advancing through the needed steps to setup shaders in the OpenGL host application.