In our experience the following books are the best on Christian counseling.
AACC Ethics Book: The Ethical Code of the American Association of Christian Counselors can be downloaded for free at http://www.aacc.net/about-us/code-of-ethics/.
Faith Therapy: Discusses the need, place, and structure of Christian counseling in the church derived from the Bible and based on the process of salvation by faith, how to overcome self-worth, significance, love and security, and how to treat common problems through faith.
Transformation: This book contains a comprehensive plan for Christian counseling derived directly from the Bible, in-depth biblical answers for complex psychological problems, models and quick reference guides for counseling 20 of the most difficult problems in the church today.
Principles for Life: Teaches 44 biblical principles and how to use them to construct Christian counseling plans to resolve problems not directly covered in the Bible.
Christian Counseling: An overview of Christian counseling.
Competent Christian Counseling: A counseling manual by the president of AACC.
How People Grow: Analysis of the counseling process by the authors of Boundaries.
Effective Biblical Counseling: The classic book on counseling by Dr. Crabb.
Basic Attending Skills: Discusses the basic listening skills. (Secular)
Basic Influencing Skills: A second skills book on basic influencing sikills. (Secular)
Private Practice Made Simple: How to start your private practice. (Secular)
The Clinical Documentation Sourcebook: Forms on CD for your private practice. (Secular)