If you're looking for a good challenge book, I highly recommend We Dare You by Kristina Contes, Meghan Heath Dymock, Genevieve Simmonds, and Nisa Fiin. It challenges you to scrap the good, the bad, and the ugly. It's a subject based book, rather than a sketch challenge. I find their ideas refreshing and unique. I have tried three so far with amazing results. They also have some great techniques that will inspire you to stretch your scrapping wings. Cost: $20 CAD. But who can really put a price on inspiration? I plan to try all of the We Dare You challenges.