You may enjoy these, they are free downloads:
The Secret Oral Teachings in Tibetan Buddhist Sects
http://lib1.org/_ads/6CD622ED1F9B86BAB57D1EBC8F1AFB0D
Cutting Through Spiritual Materialism
http://lib1.org/_ads/DD44F49A204C731E9E0C7F61885C6C12
The Tibetan Book of the Dead: First Complete Translation
http://lib1.org/_ads/093BD502D561B73DDFE61435A4C48C8A