There are some fantastic books in the field of positive psychology and other general areas which are fun and easy to read. They come highly recommended by us.
Positive psychology:
by Martin E.P. Seligman Considered by most to be the grand-daddy of
positive psychology. An excellent intro.
by Mihaly Csikszentmihalyi The concept of 'flow' is a great way to view
happiness in action. This book expands on how businesses can be profitable as well as maintaining a positive influence on the world at large.
by Jonathan Haidt A great overview of
happiness through different cultures and time - incorporating an intriguing idea of universal 'truths'.
by Daniel Gilbert
A book which gives a scientific introduction as to why it can be difficult to trust your instincts when it comes to finding happiness.

General psychology:
by Malcolm Gladwell A brilliant book that makes easy work of phenomena in areas as diverse as fashion to politics.
by Judith Rich Harris A fascinating book that explodes the myth about how important parenting is compared to peer influence in the development of children.
by Robert Cialdini Absolutely essential reading for anybody interested in psychology. A true delight.
by Daniel P. Goleman For those interested in the particulars of how emotion works in the brain - deeply insightful.