As someone who is passionate and thoroughly interested about the Voice, Flute and music in general. I am always excited when I can get my hands on a really good book that will help enlighten my mind about music. Even though I have been doing this job (although, I tend to say musical lifestyle) for over a decade, I never stop learning. Three books that I can recommend are the following:
The Voice Book by Kate DeVore and Starr Cookman
This is an excellent book. Kate and Starr are performers and Speech Language Pathologists explain things thoroughly and the accompanying CD is a wonderful tool. However, it does not replace 'in person' vocal lessons. The role of a good vocal coach/teacher is to be able to pick out nuances in your voice and anything that may not be working properly. Doing your own training by just reading a book is not the most beneficial appraoch, but a good supplement.
The second book I would recommend is, the "Inner Game of Music" by Barry Green. Although, this book was written in the 1980's it is still relevant for today. This book touches upon the psychology of being a budding professional musician, our thought process and our self-talk. Green looks at the challenges we face as musicians and how to overcome them; especially things like performance anxiety and better practice management.
Lastly, the third book I would recommend, if you are a music aficionado is Norton Anthology, A History of Western Music. It is one of the Bible's of Music History, starting from the Middle Ages all the way until the 20th Century. It is an outstanding piece of work that deals with the Ancient Greeks to Medieval/Renaissance, Baroque/Classical, Romantic to the end of 20th Century; looking at Opera, Symphonies, Jazz to Ragtime and so much more. The illustrations are absolutely incredible and there is also an accompanying CD book if you wish to purchase as well. This is an expensive book, but well worth the investment.