T'ai Chi Ch'uan by Jeaneane Fowler and Shifu Keith Ewers is a gem of a book.
It is an exploration of Taoism and T'ai Chi, with chapters on Taoist philosophy, principles, the I-Ching, energy circulation, the 13 "postures" and the simplified 24 step form. There is really a lot of information in this book that you might normally find by having to combine other books.
It is a blend of academic writing and the practice of T'ai Chi Ch'uan and the academic side really shines through for me.
It is published by Sussex Academic Press - ISBN 1-903900-20-4