I'm in absolutely no position to recommend Yoga books, as I have only read a few, but I'll be glad to share what little I know here.
In terms of Yoga training, practicing the poses, and trying to get them right, I believe "Light on Yoga" by B.K.S. Iyengar is considered a classic in the field. I often thumb through it as I practice various poses, and want to make sure I'm doing them right.
Another great book for learning the poses is "Yoga, The Iyengar Way", by Silva Mehta, Mira Mehta, and Shyam Mehta. This book offers good pictures and brief discussions of each pose, along with recommended practice sequences in the back of the book.
B.K.S. Iyengar also has another book titled "The Tree of Yoga", which discusses yoga philosophy, but I have only just thumbed through this book, so I can't comment on it too much yet, other than to say that I have enjoyed what I've read so far.
I do have several other yoga books, and I will comment on them as I read them more, but I hope this provides a good start for you.
Namaste.