Soft Shadow Mapping Using Percentage Closer Filter
- Compares various approaches to using GLSL for soft shadow mapping and refraction techniques.
- http://www.cs.utah.edu/classes/cs5610/projects-2005/lha/

Shadow Mapping Tutorial Using GLSL
- Sample renderings and code for shadow mapping.
- http://www.cs.cmu.edu/afs/cs/academic/class/15462/web.06s/asst/project3/shadowmap/

The OpenGL Shading Language Specification
- Detailed documentation on the GLSL language. Includes standard variables, constants and functions.
- http://www.opengl.org/registry/doc/GLSLangSpec.Full.1.20.8.pdf

NVIDIA SDK 9.51 Code Samples
- nVidia's OpenGL SDK. Includes code, Windows binaries and rendered examples of GLSL.
- http://http.download.nvidia.com/developer/SDK/Individual_Samples/samples.html

OpenGL Shading Language Tutorials and Demos
- ClockworkCoders's guide to GLSL. Includes a gallery, sample code, tips & tricks.
- http://www.clockworkcoders.com/oglsl/index.html

GLSL Shaders - Introduction
- Primer for using GLSL. Includes a gallery and sample code for a fractal noise generator.
- http://www.davidcornette.com/glsl/

Create Digital Motion
- The blog offers comments, examples and news regarding GLSL.
- http://createdigitalmotion.com/tag/glsl/

Wikipedia: GLSL
- A brief history, list of GLSL datatypes and explanation of variable types.
- http://en.wikipedia.org/wiki/GLSL

The Art of Texturing Using The OpenGL Shading Language
- oZone3D's tutorials for using GLSL for dynamic texturing. Includes environment mapping, glass mapping and alpha mapping.
- http://www.ozone3d.net/tutorials/glsl_texturing.php

GLSL - An Introduction
- A quick introduction to GLSL, including code snippets for common shader operations.
- http://nehe.gamedev.net/data/articles/article.asp?article=21

GLSL Tutorial
- Primer for GLSL beginners: pipeline diagrams, documentation and sample code.
- http://www.lighthouse3d.com/opengl/glsl/

GLSL Quick Reference Guide
- A PDF chart listing standard GLSL variables and constants.
- http://mew.cx/glsl_quickref.pdf

3DLabs OpenGL 2.0 Shading Language
- OpenGL Shading Language information.
- http://developer.3dlabs.com/openGL2/

3D shaders
- Online home of the OpenGL Shading Language (orange) book
- http://3dshaders.com/