This is it, the book, the "bible" of natural pregnancy avoidance and achievement, the best guide to understanding your fertility and body.  

Okay, so we're biased, but this is what other people have said, we're only repeating it.  Taking Charge of Your Fertility is the most influential book in woman's health today, and for good reason.  Toni explains women's fertility in clear language that is enjoyable to read. She includes lots of illustrations to make the concepts easy to understand and follow.  She writes from the perspective of someone who has used the method for years, herself.  This is the 2001 revised edition, which in addition to the text of the classic, includes 100 additional pages addressing fertility conditions and treatments, fertility drugs, and new charting methods.

This book is the basis for Taking Charge of Your Fertility Software, and Toni herself is a co-founder of Ovusoft, the developer of the software .  If you are using TCOYF and haven't read this book, then you should definitely give it a look.
 

Dr. Shettles outlines a method used for pre-selecting the sex of your child by timing intercourse with respect to ovulation. This is based upon studies of the vitality and motility of X-chromosome (female) and Y-chromosome (male) sperm. The reader should be advised that while there are those who swear by Dr. Shettles' method, there are researchers who claim that timing intercourse around ovulation has no impact on the gender of the child.
 

If you are interested in learning about sympto-thermal natural family planning and the moral aspects of it, this book is a good choice. Mr. & Mrs. Kippley were the first to publicize and promote the method on a large scale through their non-profit organization "The Couple-to-Couple League." This book is the reference textbook used by the League in its classes.
 

The Garden of Fertility is a guide to using fertility awareness-that is, reading fertility signals in order to prevent or achieve pregnancy. Certified fertility educator Katie Singer explains how to observe and chart fertility cycles to determine when a woman is most fertile to increase chances of conception, or to exercise birth control naturally-a method that, when followed precisely, is as effective as the Pill. Unlike other books on fertility awareness, The Garden of Fertility also describes how to use the charts to gauge gynecological health and offers nonmedical options for strengthening reproductive wellness. This book provides all the information women never learned in sex education class, but should have.