Blink is a book about “thinking without thinking” but really, it’s about how the vast majority of thinking works. The insight in this book is especially useful when dealing with people who aren’t particularly well equipped to discuss their subconscious reactions to something relatively subjective…like design.
100 Things Every Designer Needs to Know About People is a list of all the bits of psychology that they should be teaching in design school. It’s neatly organized, easy to refer to, and easily the best $30 I’ve spent on books in the last few years. If you’re even remotely interested in improving the effectiveness of your designs through an understanding of cognition, this is a great place to start.
Buy-ology is summary of a series of fMRI (Functional Magnetic Resonance Imaging) tests designed to test the effectiveness of modern marketing techniques, as well as some traditional marketing axioms. He also tackles some interesting topics like the similarities between brands and religion, subliminal advertising, and why scents may become the logos of the future.
Jonah Lehrer’s How We Decide is a dissection of the unconscious systems we use to make decisions. He takes us through the impossibly complex system of rewards that form our emotional decision making system and ultimately make us supremely efficient decision makers, even if it seems like we make bad decisions all the time. Awareness (I won’t say understanding) of these systems is incredibly enlightening for designers.