Books by the authors
Sketching User Experiences: The Workbook – Greenberg, S, Carpendale, S., Marquardt, N. and Buxton, B. Morgan Kaufmann Press. 2012
This web site is centered around this book. Definitely worth buying!
Sketching User Experiences: Getting the Design Right and the Right Design. – Buxton, B. Morgan Kaufmann Press. 2007
The companion to the workbook and a must read. This excellent, entertaining and informed book describes the why and much of the how of sketching for user interface design experiences.