NeHe of course: http://nehe.gamedev.net/article/glsl_an_introduction/25007/
Then the DGL wiki: http://wiki.delphigl.com/index.php/Tutorial_glsl
It’s german but someone else may find it interesting 😀
This one is also nice: http://www.lighthouse3d.com/opengl/glsl/
I have a very basic environment mapping shader working. I can upload it if you want.
It’s just per-vertex but it’s simple and gives nice results.