The 8 Human Talents by Gurmukh Kaur Khalsa. A wonderful book describing the main chakra energy centres of the body and their positive beneficial attributes.
Light on Life. The Yoga Journey to Wholeness, Inner Peace and Ultimate Freedom by B.K.S. Iyengar. This one little book helped me to transform my yoga practise from its mere physical elements to something much more spiritual, to learning how to reach out from my heart and core. Iyengar is true inspiration considering his humble and challenging beginnings. In fact, I would recommend most books by him.
A New Earth by Eckhardt Toll. This book spoke volumes to me about the ego, the mind and living simply in the NOW.
The Mirror of Yoga. Awakening the Intelligence of Body and Mind by Richard Freeman. Much of text is from his 6-CDs The Yoga Matrix – but I have no other teacher (so far) like Richard Freeman who can weild sensitivity, knowledge, truth and humour about the practice. Definitely top of the list.
Power Yoga, Beyond Power Yoga and Boomer Yoga by Beryl Bender Birch. She is one of my teachers, she is warm, compassionate and quite a character. She has a great way of making the yoga practice and philosophy accessible to anyone.
Ashtanga Yoga. The Practice by David Swenson. Most informative and useful book on the Ashtanga primary and secondary series.
Chants. I could recreate the wheel, but this is an excellent resource to learn and listen to the chants used in yoga, from The Yoga Workshop, Richard Freeman, Boulder CO,.