A number of volumes have contributed to my instruction in the non-dual way of thinking, many of which are listed below.
Monism related reading:
The Holy Bible KJV
The Nondual Teachings of Christ. By Charles Limcango
Non-Dual Teachings of the Bible by Galen Sharp
Nonduality I and II by Joshua Norager
36 Non-dual Exercises by Joshua Norager
10 Non-dual Meditations by Joshua Norager
The Crowd is Untruth by Soren Kierkegaard
The Sevenfold Peace Translated and edited by Edmond Bordeaux Szekely
Essene Revelation: Lost Scrolls of the Essene Brotherhood Translated and edited by Edmond Bordeaux Szekely
The Nondual Tao Te Ching by L.C. Kotlar
Advaita Made Easy by Dennis Waite
The Concept of God in Advaita Vedanta by Swami Bhaskarananda
The Journey from Many to One by Swami Bhaskarananda
The Essential Vedanta by Eliot Deutsch
Vedanta: Voice of Freedom by Swami Vivekananda
Beyond Good and Evil by F.W. Nietzsche
Jesus: From Enoch to the Dead Sea Scrolls Translated and edited by Edmond Bordeaux Szekely
Nondual Perspectives on Quantum Physics: A Guide to the Yoga of Knowledge
Monism as Connecting Religion and Science by Ernst Haeckel
Mind and Motion and Monism by George John Romanes
Dancing Beyond Thought by Gary Weber, Ph.D
The Whole Truth: The Core of Ultimate Understanding by Ramesh S. Balsekar
Banus The Essene Translated and edited by Edmond Bordeaux Szekely
The Secret Doctrines of Jesus by H.S. Lewis AMORC
The Celestine Prophecy by James Redfield
A Gnostic Prayer Book by Surekha Minati Keerthana
The Gospel of Thomas by A. Nyland
Gnostic Meditation: A Manual by Luis Varady
The Eye of the I From Which Nothing is Hidden by David R. Hawkins MD, Ph.D.
Atma Bodha by Gireesh Haridas
Translation of the Sikh Religion Holy Scriptures by Sri Guru Granth Sahib
Quran: English Translation by Talal Itani
Sufi Meditations by Ibn 'Ata' Allah of Alexandria
The Courage to be Disliked by Ichiro Kishimi and Fumitake Koga
Talks on Self Enquiry: Atma Vichara According to the Teachings of Ramana Maharshi by Miles Wright
Tips for Evolved Spiritual Living by Sri Vishwanath
The Essenes and the Sacred Scrolls from the Nag Hammadi and the Dead Sea by Anthony Mountain
The Essene Science of Fasting Translated and edited by Edmond Bordeaux Szekely
The Essene Gospel of Peace Translated and edited by Edmond Bordeaux Szekely
Psychology/Philosophy reading:
Group Psychology and the Analysis of the Ego by Sigmund Freud
The Black Science by Dr. Haha Lung and Chris Prowant
The Holy Science by Jnanavatar Swami Sriyukteswar Giri
Dualism and Mind by Scott Calef @ Ohio Wesleyan University, U.S.A. Http://www.iep.utm.edu/dualism
The Complete Works of Plato Translated by Benjamin Jowett
The Crowd; Study of the Popular Mind by Gustave Le Bon
The Group Mind: A Sketch of the Principles of Collective Psychology by William McDougall
The Ego States by Catherine Holden
Steppenwolf by Hermann Hesse
Siddhartha by Hermann Hesse
Ueber die Grenzen des Naturerkennens – Die Sieben Weltraetsel by Emil du Bois-Reymond
Victim of Thought by Jill Whalen
Thus Spake Zarathustra by F.W. Nietzsche
The Power of the Subconscious Mind and Other Works by Joseph Murphy
The Triune Brain, Hypnosis and the Evolution of Consciousness by Adam Weishaupt
Secrets of the Rosicrucian & Christian Scientists Revealed by Chet Dembeck
The Forbidden Religion by Jose M. Herrou Aragon
Trial of the Witnesses of the Resurrection of Jesus by Thomas Sherlock
Wherever You Go, There You Are. Mindfulness Meditation in Everyday Life by Jon Kabat-Zinn
The Best of Thich Nhat Hanh – Life Lessons, Inspiration And Best Quotes by Jordan Baker
Modern Buddhism The Path of Compassion and Wisdom by Geshe Kelsang Gyatso
The Rosary of the Philosophers by Arnaldus de Villa Nova
200 Golden Hadiths from the Messenger of Allah (SAW) by Abdul Malik Mujahid
The Tibetan Book of the Dead Edited by John Baldock