Eden Gray's "Mastering the Tarot" was my first, too. It's a decent enough starter, but the one that really started making things click for me was the book that comes with Mythic Tarot by Juliet Sherman-Burke and Liz Greene.
After having read many a book on tarot my two favorites are "Tarot and the Journey of the Hero" by Hajo Banzhaf for the Majors and "Tarot and the Tree of Life" by Isabel Radow Kliegman for the Minors.
Most importantly, I recommend that all tarot reader look for information outside of tarot to assist them in their readings. Studying astrology can be a great asset, since it gives you an idea the the querents personality right from the get-go (remember to ask them their birthday). This also comes in handy when reading with decks like Thoth, and others that are replete with astrological symbols. I didn't get into astrology until after I started studying tarot. However, I had studied various personality typing systems. My favorite is the Enneagram. "Personality Types" and "Wisdom of the Enneagram" by Don Richard Riso and Russ Hudson are my main recommendations. While a reading may not necessarily tell you one's specific type, if the reading clues you into an issue that tends to be found in a certain type, other issue of that type may be needed to be dealt with by the querent. Also, if reading for a friend, who's type you may very likely be able to figure out, then you may be able to present ideas to them that they may not otherwise listen too. Never underestimate outside sources of information for readings!
As far as books I'm not too keen on, the one that just out is "The Tarot Handbook" by Angeles Arrien. I got it because other readers recommended it to me. However, I was rather disappointed. I do like her descriptions and commentaries on the various symbols in the artwork of the cards (Thoth deck). What I really don't like is her trying to make to divinatory meanings of the cards so cut and dried. Attempts to make cut and dried systems in respect to a number signifying that many days, weeks, or months or astrological symbolism specifically pertaining to a person born under that sun sign, DO NOT WORK when doing readings. Crowley himself in "Book of Thoth" (part very profound ideas; part pseudo-mystical secret-code junk) talked about the importance of not taking symbols literally, and that it was obviously stupid to do so. I also don't particularly like her, personality card and soul card systems. I find all the Tarot archetypes to be a part of the psyches of all people; however invisible some may sometimes be.
Okay that's enough rambling on for me!
Love, understanding, and compassion,
Matt