Here are a number of wonderful books to help broaden and deepen your knowledge and experience of yoga:

Calais-Germain, Blandine. Anatomy of Movement. Eastman Press. Seattle, Washington, 1991.

Desikachar, T.K.V.  The Heart of Yoga: Developing a Personal Practice.  Inner  Traditions International.  Vermont, USA.  1995.

Feuerstein, Georg. The Yoga Tradition. Hohm Press. 2001.

Frawley, David.. Yoga and Ayurveda:  Self-Healing and Self-Realization. Lotus Press.1999.

Iyengar, B.K.S. Yoga The Path to Holistic Health. Dorling Kindersley. London, England, 2001.
-other books by Mr. Iyengar are Light on Yoga, Light on Pranayama and Light on the Yoga Sutras of Patanjali..

Kraftsow, Gary. Yoga for Wellness: Healing with the Timeless Teachings of Viniyoga.  Penguin Group. 1999.

Lad, Dr. Vasant. Ayurveda: The Science of Self-Healing. Lotus Press. 1984. 

Lasater, Judith. Relax and Renew: Restful Yoga for Stressful Times.  Rodnell Press. California, 1995.

Prabhavananda, Swami and Christopher Isherwood. How to Know God: the Yoga Aphorisms of Patanjali.  Vedanta Society of Southern California, 1981.
-excellent translation of the Yoga Sutras, considered the foundation for the practice of yoga in the West. It outlines the 8 limbed path of yoga
Translations of the sutras are also found in The Heart of Yoga and The Yoga Tradition.

Radha, Swami Sivananda. Hatha Yoga: the Hidden Language - Symbols, Secrets and Metaphor.  Timeless Books, 1995.
-wonderful exploration of the meaning behind various yoga postures

Schiffman, Erich. The Spirit and Practice of Moving into Stillness. Pocket Books. New York, New York, 1996.