The definitive resource for the field, Principles and Practice of Stress Management, 2nd Edition, is the only complete stress management reference in which methods are described by the author most closely associated with an established technique.
Awesome overview of many of the relaxation methods available, including reviews of the effects of those study and scientific studies to quantify impact. If you're looking for a high level overview of the practice of yoga or bio-feedback or buddhist meditation, this is the book to check.