I recently bought a copy of Autostretching by Olaf Evjenth and Jern Hamberg. It’s a Norwegian publication but is written in English
http://www.optp.com/shop.cfm?groupid=Stretching&catid=Resources
This is far and away the most detailed book on stretching I have come across. It particularly excels at stretches for the spine and neck. The book shows the specific muscle(s) being stretched, gives detailed cues, and describes common technique mistakes that really make the difference. I think the hamstring stretches are a little aggressive, as they require more of a lunging position rather than supine. However, most of the stretches shown are very effective, especially when it comes to zeroing in on the little nagging muscles (e.g., in the neck) that never seem to get hit by more coventional stretches. The calf and ankle stretches have been among the most effective that I have used and have really helped me with problems in that area.
This is a definite buy for anyone looking for new ideas on stretching and well worth the money.