Yes there are two outstanding books on flexibility.

1: Stretching Scientifically by Thomas Kurz

Learn…

How to stretch safely and quickly to achieve and maintain your maximum flexibility
How to make your muscles grow stronger and longer so you stay flexible all the time
How to do splits even if you are over 40 or 50
How to kick high and do splits with no warm-up
How to develop each of the three kinds of flexibility—dynamic, static active and static passive—to suit every athlete’s needs
What exercises are “no-no’s” if you want to stretch your muscles
All the factors limiting flexibility
Brilliantly simple tests of hip joint mobility and muscle length that dispel common misconceptions of what limits flexibility the most

http://www.stadion.com/stretch.html

2: Relax into Stretch by Pavel Tsatsouline

How the secret of mastering your emotions can add immediate inches to your stretch
How to wait out your tension the surprising key to greater mobility and a better stretch
How to fool your reflexes into giving you all the stretch you want
Why contract-relax stretching is 267% more effective than conventional relaxed stretching
How to breathe your way to greater flexibility
Using the Russian technique of Forced Relaxation as your ultimate stretching weapon
How to stretch when injured faster, safer ways to heal
Young, old, male, female learn what stretches are best for you and what stretches to avoid
Why excessive flexibility can be detrimental to athletic performance and how to determine your real flexibility needs
Plateau-busting strategies for the chronically inflexible.

http://www.dragondoor.com/b14.html