This one is sort of a no-brainer for The Daily Doubter, but the best doubt related book I've read in the past year has to be Doubt: A History by Jennifer Michael Hecht. This is an amazing book that, as the title suggests, chronicles the global history of doubt and disbelief. In this work Hecht portrays doubt not as a negative force, but as a positive and creative tool that has generated discovery by driving individuals to think and question accepted thoughts about the world around them. Readers will be impressed with the rich history of doubt that extends from the time of the ancient Greeks all the way up to the present - and unlike many historical works Hecht does not focus simply on Western thought, but also traces doubt through eastern theology and philosophy.
The fact that it was six months ago that I finished this book coupled with my laziness does not allow me to do this work the justice of a proper review, so I will here defer to Tim Callahan's extensive eSkeptic review.