I have read Dan Barton's book, and I thought it was very informative, but I have to say I am far more impressed with Bonsai, its Art, Science, and philosophy by Deborah Koreshoff. It is so detailed, and I am only half way through it!! The one thing I loved about Dan Barton's book is the how to make a crescent pot out of fibreglass. very handy to know

I have had a quick flick through David Joyce's book also, and that seems quite detailed too. Is it just me or do all bonsai authors make their own pots too??
Paddles,I have found there are plenty of books aimed at beginners, and only a few aimed at the advanced bonsai artist. I started at my library and they had only basic beginner books which all seem to cover the same thing (history, styles, suitable trees, how to wire etc) But then you read more specialised books like Peter Adams books (eg The Art of bonsai - Peter D Adams or bonsai with Japanese Maples) and like you say, you need a firm understanding, and even then you need to concentrate. But I have found that if I learn only one thing from a "beginner book", then it is worth while. I now have a shelf dedicated just to bonsai books.
My collection consists of -
Bonsai with Japanese Maples - Peter Adams (read and highly recomend)
The Art of Bonsai - Peter Adams (read and highly recommend )
Bonsai, its art, science, history and philosophy - Deborah Koreshoff (reading atm, but very detailed..... a must have)
The bonsai book - Dan Barton (read, would recommend)
The Art of Natural Bonsai - David Joyce (yet to read)
The complete book of bonsai - Harry Tomlimson (Yet to read)
A guide to Bonsai - Peter Chan (read and whilst not as detailed I would have liked, it covers topics that more basic books don't)
The living art of Bonsai - Professor Amy Liang (Yet to read)
The secret techniques of bonsai - Masakuni Kawasumi II & III (yet to read)
Bonsai - Linda M. Walker (op shop find) (yet to read)
Step-by-step Guide to growing Bonsai trees - Joan Melville (op shop find) (yet to read)
Post dated - The schooling of an Irreverent monk - Michael Hagedorn (read, very informative, but bewarned, you will want to study under a Bonsai Master in Japan after reading this)
Bonsai Today issue # 12 (read, excellent info on growing seedlings)
I have read countless others including John Naka's bonsai Techniques and others from my bonsai club's library but I can't recall names and authors. I will be adding Bonsai Techniques to my collection when money permits
I will up date this post as I finish each book, or add to the collection
Enjoy
