"The Pictorial Key to the Tarot" Book by A.E. Waite, Best Into Text
Waite worked with the artist Pamela Coleman Smith to create the most popular tarot card deck in the world. He wrote this book to explain the symbolism and uses of the deck.
The book is broken into three parts: "The Veil and Its Symbols" which provides a history of the tarot along with traditional symbols associated with each card; "The Doctrine of the Veil" comprising 78 black and white images of the Rider-Waite deck along with regular and reversed meanings; and "The Outer Methods of the Oracles" which discusses the art of tarot divination, including the now famous Celtic Cross Spread.
This is the single most useful book for learning to interpret the cards. Lessons learned with this book can be applied to other tarot card decks.