Hey im busy using GIMP at the moment to make head textures and ive been having throuble making nice smooth shading that look realistic. I'm hoping you guys can give me some good advice on how to shade, and maybe some tools im GIMP that would be helpful. To shade at the moment i use the airbrush tool, using a black or white colour depending on it im highlighting or shadowing, and a lower the opacity according to how hard i want the shadow. Then if it looks uneven or somthing i bring out the smudge tool and try smooth it out abit. Heres a zoomed in bit f my previous work to help you guys.
http://imageshack.us/photo/my-images...mpleshade.png/

shading huh? uummm, here, this is wat I usually do....
Ctrl+L the click the layer you want to shade then right click>alpha to selection the right click on the image>shrink..... play with those for a while and the make a new layer by pressing ctrl+shif+n and color the layer with a brighter color then gaussian blur it.....
For the tools you can use dodge/burn tool and airbrush tool....