I will add to this list as I work my way through the various books I encounter in my studies.
Abbott, John S. C., The History of Christianity. Portland, ME: G. Stinson, 1883.
Bainton, Roland H., The Church of Our Fathers. Philadelphia, PA: The Westminster Press, 1941 and 1950.
Bass, Diana Butler, A People’s History of Christianity. New York, NY. Harper Collins Publishers, 2010.
Guericke, Heinrich E. F., translated from the German by William G.T. Shedd, A Manual of Church History. Boston : Draper and Halliday ; New York : Hurd & Houghton, 1867, 1857
Grun, Bernard; The Timetables of History. New York, NY. Simon and Schuster/Touchstone, 1946, …1991.
Hennecke, Edgar and Schneemelcher, Wilhelm; New Testament Apocrypha. Volume One: Gospels and Related Writings. The Westminster Press, Philadelphia, 1963.
Nouwen, Henri J. M; Spiritual Formation: Following the Movements of the Spirit. Harper Collins, 2010.
Smith, Huston; The Soul of Christianity: Restoring the Great Tradition. Harper Collins, New York, 2005.
Staniforth, Maxwell (translator); Early Christian Writings. Penguin Books, London, 1968.
The Church, A Trilogy. This is a reprinting of three books by the Christian Restoration Association, 2000.
– Shannon, Robert C., The New Testament Church. Originally published by Standard Publishing, 1964, and College Press, 1984.
– Wade, John W., The Church Through the Centuries. Originally published by Standard Publishing, 1964.
– Dowling, Enos E., The Restoration Movement. Originally published by Standard Publishing, 1964.
Twitchell, James B., Shopping for God. Simon and Schuster, New York, 2007.
Viola, Frank and Barna, George; Pagan Christianity? Exploring the Roots of Our Church Practices. Tyndale House Publishers, 2002 and 2008.
Wegner, Paul D; The Journey from Texts to Translations. Baker Academic, Grand Rapids, MI, 2000.
For more about Gnosticism and the Gnostic writings:
Bock, Darrell L., PhD, Breaking the Da Vinci Code. Nashville, TN: Thomas Nelson, Inc., 2004
Hoeller, Stephan A., Gnosticism, New Light on the Ancient Tradition of Inner Knowing. Wheaton, IL: Quest Books, Theosophical Publishing House, 2002.
Pagels, Elaine, Beyond Belief, The Secret Gospel of Thomas. New York, NY. Random House, 2005.