With some reservations, I suggest this one: http://www.diycosmetics.com/the-supe...soap-naturally
The authors touch on a wide variety of subjects that would interest an intermediate or advanced soaper, and I am certainly learning more about butter soap, liquid soap, and different methods of HP and CP soap making. I find myself nodding and thinking "Hmmm, that's good to know!", but unfortunately I would read on and grind my teeth in frustration.
The authors discuss some topics beautifully, but others in confusing and overly-complicated depth. Still more topics they dismiss after a brief explanation and airy dismissal, which was annoying to me. They also present some information as "facts" that I felt were personal beliefs or were theories not well supported by science.
The authors have a companion recipe book that is not yet published, and they refer the reader in several places to the recipe book for detailed information on making a particular soap. I found that frustrating. I would have preferred to see a basic recipe given in THIS first book for a particular soap or soaping technique, and then refer the reader to the second book for options, etc.
I would never give this book to a beginner, even though the book contains step by step tutorials. There are few illustrations that is a disadvantage to many beginners -- a picture, 1000 words, and all that. Some tutorials refer the reader back to an earlier tutorial to avoid repeating information. While I see the point in doing that, the practice is awkward and not helpful to a beginner, especially since they don't give a page number reference. I also think the confusing way that some information is presented could be a turn off to some beginners.
This book will stay on my bookshelf as a reference. But I will use it to supplement my knowledge, not be my main source of information.