The Collected Works of Sri Ramana Maharshi - This book contains the original works of Srī Ramana, as well as translations of other non-dual texts.
I Am That - Srī Nisargadatta Maharaj's teachings on Self-Enquiry.
Yoga Vasiṣṭha - A classic text that explains Non-dual Vedānta philosophy in the form of the sage Vasiṣṭha's lectures to Śri Rama over the course of 22 days, which resulted in Rama's enlightenment. This is a condensed version (the original being quite long at 32,000 verses) that presents the main principles of the original along with the stories that illustrate them.
Advaita Bodha Deepika - The Lamp of Non-Dual Knowledge, by Srī Karaptra Swami, translated into English by Srī Ramānanda Saraswati, a devotee of Srī Ramana Maharshi.
The Impostor - An article on ego, thought, and the Self.
The path to awakening is not new; it has been practiced by seekers of Truth for thousands of years. By studying different spiritual systems, the universal nature of this path becomes evident. These websites represent both "traditional" and "contemporary" practices.
Ch'an Buddhism - The teachings of the Buddha according to the Ch'an (Chinese Zen) School of Buddhism.
headless.org - Teachings of Doulas Harding who created several experiments designed to help the seeker develop a true perspective.
nimatullahi.org - Principles and practices of the Sufi path to Oneness. The Sufi path is the path of spiritual devotion.
selfdiscoveryportal.com - Extensive website with articles on the path of Self-inquiry from Art Ticknor, a student of Richard Rose.
sivanandonline.org - Website of the Divine Life Society, founded by Swami Sivananda, contains several articles on the principles and practices of Yoga and Vedānta.
swamij.com - Website of the Swami Jnaneshvara Bharati containing extensive information on the principles and practices of traditional Yoga.