Other Lives, Other Selves: A Jungian Psychotherapist Discovers Past Lives - Roger Woolger, PhD, (Doubleday), 1987.
After reading what is popular today as well as past writers (not naming names) I find that Dr Woolgers work is the most comprehensive approach to Past Life Therapy available. While many using hypnosis place an emphasis on recovering the memory, Dr Woolger's experience is that the memory is the least difficult part of regression process, guiding the traumatic experience and wound to the soul to resolution and healing is the cornerstone of his work. This is the piece, personally that I see lacking in other approaches. His work is founded in sound psychological AND spiritual principles and the ability to synthesize this and make it practical and accessible is clear in this book.