It seems obvious that Jim Gorham should put one out. The most popular style is the complex mandala intricate variety.
Jim's decorative fantasy heads might play huge. Plus he has the skills for clean illustrator line art.
I've been dabbling myself with a coloring book approach.
Being led there by the Enworld freelance, wanting to start cleaner before I got into photoshop for color.
I'm using the freeform pen tool in photoshop and a couple of actions to make it easier to work efficiently.