I found an amazing thing today: a tutorial on painting that shows the evolution of the cover art for Moon Called by Patricia Briggs. It is direct from the artist of the piece, Dan Dos Santos, and is intended as a tutorial on painting, but it is an amazing find for anyone interested in book covers, art, or Moon Called in particular.
Dos Santos turned the tutorial into a PDF document that you can read online. It is very extensive, with 15 steps and lots of art. Quite fascinating. Go check it out NOW.