Many 
people seem (justifiably) enamored with Eric Fortune's The Red Magician. Here is a progression from sketch to finish. In art school they tell you that a painting should slowly evolved from the ground up. Of all the illustrators I know, only Eric and David Bowers actually to paint like that. Eric's patience pays off -- all that layering creates a glow and a subtlety to the surface that is just remarkable. Thumbnail interview with Eric here.