The design details
For anyone who builds apps, websites or services this is a must read. In this book Dan Saffer, presents the notion of microinteractions. These are the smallest interaction possible. Saffer also presents products that consist of only one microinteraction. These examples are inspiring for any creator because they help to have an extreme and sharp focus.
This book presents a set of theories that every designer should have at least seen once. So get it and read it.