Books
Introductory
Reverend Jaganath Carrera, Inside the Yoga Sutras: A Comprehensive Sourcebook for the Study and Practice of Patanjali's Yoga Sutras (Integral Yoga Publications 2006)
Nischala Joy Devi, The Secret Power of Yoga- A Woman's Guide to the Heart and Spirit of the Yoga Sutras (Three Rivers Press 2007)
Sri Swami Satchidananda, The Yoga Sutras of Patanjali (Integral Yoga Publications 1978)
I.K. Taimni, The Science Of Yoga (The Theosophical Publishing House)
Intermediate
B.K.S. Iyengar, Light on the Yoga Sutras of Patanjali (Thorsons 1996)
Sri Swami Krishnananda, "The Yoga System" (The Divine Life Trust Society 1981) (http://www.swami-krishnananda.org/yoga_00.html)
Sri Swami Krishnananda, The Study and Practice of Yoga -An Exposition on the Yoga Sutras of Patanjali (The Divine Life Society) (http://www.swami-krishnananda.org/patanjali/Study_and_Practice_of_Yoga_Volume-I.pdf)
Sri Swami Rajarshi Muni, Yoga The Ultimate Spiritual Path (Llewellyn Publications 2001)
Sri Swami Vivekananda, Sutras- Sanskrit Text with Transliteration, Translation & Commentary (Unknown publisher, http://www.scribd.com/doc/22604552/Patanjali-Yoga-Sutra-Swami-Vivekananda)
Advanced
Sri Aurobindo- The Synthesis of Yoga (Sri Aurobindo Ashram Trust 1999)(http://www.sriaurobindoashram.org/ashram/sriauro/writings.php)
Georg Feuerstein, The Yoga Sutras of Patanjali: A New Translation and Commentary (Inner Traditions International 1979)
Chip Hartranft, The Yoga Sutras of Patanjali: A New Translation with Commentary (Shambhala Classics 2003)
Sri Swami Krishnananda, The Study and Practice of Yoga (The Divine Life Society) http://www.swami-krishnananda.org/patanjali.html
Ian Whicher, The Integrity of the Yoga Darsana- A Reconsideration of Classical Yoga (State University of New York Press 1998)
James Haughton Woods, The Yoga-System of Patanjali (Or the Ancient Hindu Doctrine of Concentration of Mind Embracing the Mnemonic Rules, Called Yoga-Sutras, of Patanjali and the Comment, called Yoga-Bhashya, Attributed to Veda-Vyasa and the Explanation, called Tattva-Vaicaradi of Vachaspati-Micra) (The Harvard University Press, 1914)
Websites
Satchidananda Ashram-Yogaville (http://www.yogaville.org/)
Parmarth Niketan Ashram (http://www.parmarth.com/home.html)
The Divine Life Society (http://www.dlshq.org/) (See "Free Book Distribution" on the Homepage)
Sri Aurobindo Ashram Website (http://www.sriaurobindoashram.org/) (See "Selected Works" on the Homepage for a free collection of almost all of Sri Aurobindo's writings in PDF form)
Arunachala & Bhagavan Sri Ramana Maharshi (http://www.arunachala-ramana.org/index.htm) (Information about the Ashram and an archive of free works in PDF form written by Sri Ramana Maharshi)
The Atma Joyti Blog- A Meditation and Practical Spiritual Life Resource (http://blog.atmajyoti.org/)
The Internet Archive of the Yoga Sutras of Patanjali, Vast archive of Translations of the Sutras in 35 languages, Commentaries, Resources, Discussion Forums, Free downloads (http://hrih.net/patanjali/)
iHanuman-Love.Service.Devotion.Yoga. (http://www.ihanuman.com/)
Carlos Pomeda Website (Website of Carlos Pomeda, a teacher of yoga and Indian philosophy) (http://www.pomeda.com/)
Sally Durgananda Kempton (Website of Sally Kempton, a teacher of meditation, tantra and yoga philosophy; Collection of articles by Sally Kempton) (http://www.sallykempton.com/home.html)
Piedmont Yoga Studio (Collection of articles by Richard Rosen, the Director of the Piedmont Yoga Studio) (http://www.piedmontyoga.com/library.html)
Sean Corn Website (Videos of Sean demonstrating Yoga Flows) (http://www.seanecorn.com/)
Puja.net (Resources on the Vedic mythology, astrology, music, mantras and rituals; podcasts, photographs and videos) (http://www.puja.net/)
Internet Sacred Text Archive (Free archive of vast collection of works on Hinduism and all wisdom traditions) (http://www.sacred-texts.com/hin/)
Swami Jnaneshvara Bharati, The Yoga Sutras, Translations, Commentary, and Illustrations (http://www.swamij.com/index-yoga-meditation-yoga-sutras.htm)
Krishnamacharya Yoga Mandiram, Chennai- The Yoga Sutra of Patanjali- Introduction and Translations (http://acharya.iitm.ac.in/mirrors/vv/scripture/yogasutra/yoga.html)
The American Sanskrit Institute- Classes on learning Sanskrit, Yoga Sutra Workshops and Multimedia Sanskrit lessons (http://americansanskrit.com/)
Heart Mind- A Huge Collection of Yoga Resources and Translations, In-Depth Commentary and Related Resources on the Yoga Sutras http://www.rainbowbody.net/HeartMind/Yogasutra.htm
Swami Rama's Video Lectures on the Yoga Sutras (Eight Lectures, 13 hours of video) (http://www.youtube.com/swamiramahimalayas)
Audio
Patanjali's Yoga Sutras by Kausthub Desikachar (Swathi Soft Solutions, 2008) (Available in iTunes Store)
Patanjali's Yoga Sutras: The Original Master's Eight Steps of Yoga (Times Music, India 2005 (Available in iTunes Store)
Translations of the Sutras, with Audio Chants of each Sutra by Mark Giubarelli (http://www.patanjalisutras.com/yoga-sutras-ch4-1-10.html)
Yoga Studios Where I Practice
Kali Ray Triyoga- Santa Cruz (http://triyoga.com/welcome.php)
Yoga Tree Yoga Center- San Francisco (http://www.yogatreesf.com/index.htm)
Los Gatos Yoga Center-Los Gatos (http://www.yogacenterlosgatos.com/)