I think the problem with GLSL is that it's not something that's easily tutorialized. You can't just put a GLSL tutorial into an engine and then expect to be able to do cool bumpy specular reflective stuff straight away on everything; a lot of it is dependent on the data that your engine hands over to the shaders, how your rendering passes are structured and so on. That's a lot of work before you even start writing shaders! All that GLSL does is (over-simplified explanation ahoy!) intercept the standard glVertex/glNormal/glColor/glTexCoord/etc calls and let you replace the canned behaviour of them with your own.
Rather than a GLSL Quake tutorial, if you're interested in learning it, you're much better off grabbing a "spinning cube" program and working on that.