Horde3D

If you have some links on GLSL shaders, please, post in this topic

http://www.ozone3d.net/tutorials/glsl_fog/index.php - In this tutorial, we shall see how to add fog support to our real-time GLSL-written shaders (OpenGL Shading Language). Fog support already existssince the first implementations of OpenGL at the fixed pipeline level, but if your objects' rendering uses GLSL shaders, you'll need to implement it at the programmable pipeline level.

For absolute beginners
http://www.typhoonlabs.com/

The 5 .pdf files will get you in to glsl in no time, they even have there own tool to test out the stuff are coding, Shader Designer.
The tool is old and a bit buggy (on my linux at least) but if you press ctrl+s once-in-a-while it will get you true the tutorials in no time.

http://3dshaders.com/home/index.php?opt ... &Itemid=34
"GLSLdemo Executable" : there are some shaders and a program to view them