Power v's Force: by David Hawkins.
Eye of the I: by David Hawkins.
I, Subjectivity & Reality by David Hawkins.
These books are a series of three in which the levels of consciousness are explained and calibrated. A technique is explained in which you can determine any thought, idea or person and whether it is true or false. Truly remarkable books.

Autobiography of a Yogi by Paramhansa Yogananda.
This is the story of Yogananda and his search for Self-Realisation, describes in detail Superconscious perception and kriya yoga

Aura and Consciousness by Konstantin Korotkov.
This book details major research into the aura and various components of states of consciousness using kirlian photography.

The Freedom of Choice by Tom Chalko
Great book on perception and spiritual development, details as the name states the significance of the freedom of choice.