I read "Mystical Origins of the Tarot" by Paul Huson, and I recommend it to anyone that wants to learn about Tarot. There are a lot of misconceptions about the Tarot and the origins of the cards, and this author did a thorough investigation, and presents all the information available, giving plausible hypothesis.
The first half of the book is about the history of the Tarot, the second half is about interpreting the cards. So you can read one part only if you don't care about the other one.