"The Book of Tea" by Alain Stella, Nadine Beauthéac et al.
If your looking for a single book about tea and you like lavishly illustrated coffee table books (no pun intended :-) ), then is THE book. Absolutely beautifully illustrated but also very well documented and complete, this book encapsulates all the aspects of tea that make it such a fascinating beverage. Culture and plantations, history and customs, taste, types, and a connoisseur's guide, nothing is missing in this book. It was my first big book on tea and it's one that I've read many times. It's still my favourite book. You can't go wrong with this one !!!
P.S. I just discovered that there is a second edition of this book which has been updated. I don't really see what could be updated beyond the connoisseur's guide. If you click on the image, it will take you straight to Amazon and give you all the details.