Several titles already mentioned are also among my top ten favorites:
Tarot: History, Symbolism & Divination - Robert Place
Mystical Origins of the Tarot - Paul Huson
Encyclopedia of Tarot, various volumes - Stuart Kaplan
Tarot Bible - Sarah Bartlett
Tarot Plain and Simple - Anthony Louis
Tarot Wisdom - Rachel Pollack
Tarot and the Tree of Life - Isabel Kliegman
Tarot: Your Everyday Guide - Janina Renee
Understanding the Tarot Court - Mary K. Greer and Tom Little
and for my tenth, I would add one that hasn't been mentioned yet:
The Complete Tarot Reader - Teresa Michelsen
An AT review of this excellent intermediate level workbook can be found here:
http://www.aeclectic.net/tarot/books/complete-tarot-reader/
Alan