the WiP of the Reventon in GIMP
hope it's gonna be helpful as a tutorial for GIMP users... I didn't use any special effects of filters, it's just a simple painting/airbrushing
art of course by me EDIT:
I just wanna let you know that you should remove the outlines after putting shadings and highlights, before doing this the outlines can help you a bit, so you can just make the outlines layer invisible or visible (depending on what are you doing now).
Shit, i've just noticed that Revvy looks freakin' flat in this picture. I knew I'll freak up something. Why can't i draw even one car perfectly...