I am currently enrolled in a Crystal Healing Practitioner Course. One of the lessons deals with Pendulum Dowsing. As a result, I have compiled a list of books here. Those denoted with an (*) are titles that I currently own.

The Art of the Pendulum: Kit by Maxi Cohen
This book is available at both Amazon (US) and Amazon (CDA).

Techniques of Pendulum Dowsing by Bill Cox
This book is available at both Amazon (US) and Amazon (CDA).

* A Little Book of Pendulum Magic by D. J. Conway
This book is available at both Amazon (US) and Amazon (CDA).

Pendulum Dowsing by Cassandra Eason
This book is available at both Amazon (US) and Amazon (CDA).

* The Practical Pendulum Book by D. Jurriaanse
This book is available at both Amazon (US) and Amazon (CDA).

* The Pendulum Kit by Sig Lonegren
This book is available at both Amazon (US) and Amazon (CDA).

* Pendulum Healing Handbook by Walter Lubeck
This book is available at both Amazon (US) and Amazon (CDA).

* Dowsing for Health: Tuning in to the Earth's Energy for Personal Development and Wellbeing
by Patrick MacManaway, Don Last and Ben Cracknell
This book is available at both Amazon (US) and Amazon (CDA).

* Pendulum Power: A Mystery You Can See, a Power You Can Feel by Greg Nielsen and Joseph Polansky
This book is available at both Amazon (US) and Amazon (CDA).

Pendulum Charts by Dale W. Olson
This book is available at both Amazon (US) and Amazon (CDA).

The Pendulum: Bridge to Infinite Knowing by Dale W. Olson
This book is available at both Amazon (US) and Amazon (CDA).

* Pendulum Workbook by Markus Schirner
This book is available at both Amazon (US) and Amazon (CDA).

* Pendulum Magic for Beginners: Power to Achieve All Goals by Richard Webster
This book is available at both Amazon (US) and Amazon (CDA).

Principles of Dowsing by Dennis Wheatley
This book is available at Amazon (US).

* The Divining Heart: Dowsing and Spiritual Unfoldment by Patricia C. Wright and Richard D. Wright
This book is available at both Amazon (US) and Amazon (CDA).