I've tried a variety of techniques, but nothing provides good line artwork. Some are fine for personal use, but I haven't found anything that produces acceptable professional results.

Below are links that I've tried.

http://www.photoshopsupport.com/tutorials/jennifer/photo-to-sketch.html

http://www.merrimentdesign.com/family-coloring-book-from-photos.php

http://www.photoshoproadmap.com/Photoshop-blog/2007/04/15/give-your-photos-a-color-ink-sketch-effect/

http://content.photojojo.com/diy/how-to-create-coloring-book-using-photos/

If anybody would like to sample coloring books that arren't just for kids, Dover Publications has an unbelievable selection, most of which can be viewed page by page with a watermark (they're part of Amazon's 4-for-3 promotion):
http://store.doverpublications.com/by-subject-coloring-books.html?_s_icmp=a1a294S8

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon