The Tibetan Book of the Dead: First Complete Translation
The Great Rebellion, Treatise of Revolutionary Psychology, The Revolution Of The Dialectic or any book by Samael Aun Weor.
How to See Yourself as You Are, A Flash of Lightning in The Dark or any book by the Dalai Lama.
Any book by Jiddu Krishnamurti.
How to Know Higher Worlds by Rudolf Stiener is pretty good.
The Gospel of Sri Ramakrishna.
Once again everything by Samael Aun Weor.
Also there is a ton of amazing free material at this non-profit site.
www.gnosticteachings.com