The Seth books by Jane Roberts─all Seth’s books. Best to start with: The Nature of Personal Reality.
Ram Dass─all his books, especially Be Here Now, Journey of Awakening, Grist for the Mill, The Only Dance There Is and his take on the Bhagavad-Gita.
Thich Nhat Hanh─all his books. Best to start with: The Miracle of Mindfulness and Transformation and Healing
Rumi─all his books. Best to start with: The Essential Rumi, translated by Coleman Barks
Ngak’chang Rinpoche─all his books: Spectrum of Ecstasy, Wearing the Body of Visions, Roaring Silence and more.
Lao Tzu─The Way of Life, the translation by Stephen Mitchell is good
Brian Walker─Hua Hu Ching: The Unknown Teachings of Lao Tzu
Bruce Kumar Frantzis─The Great Stillness, 2 volumes
Alan Oken─The Complete Astrology
Robert Hand─Planets in Transits and all his other books.
Martin Schulman─Karmic Astrology series
Also, of Interest:
Osho─The Book of the Secrets, Volumes I-V, among others
Alan Watts─Tao: The Watercourse way, among others
Chogyam Trungpa─Cutting through Spiritual Materialism, among others
David K. Reynolds─all his Constructive Living books
For more: Spiritual Practices Reading List