At its core, there are four primary branches of Yoga. Not everyone will agree with this classification, but the framework stands: Jnana Yoga, Raj Yoga, Hatha Yoga, and Bhakti Yoga.
If you find yourself drawn to Jnana Yoga, this page serves as an excellent starting point for information and literature links:
http://en.wikipedia.org/wiki/Ramana_Maharshi
For those interested in Raj Yoga, look toward Patanjali and his Yoga Sutras:
http://en.wikipedia.org/wiki/Yoga_Sutras_of_Patanjali
If your focus is specifically Hatha Yoga, you might start here:
http://en.wikipedia.org/wiki/Hatha_Yoga_Pradipika
http://search.4shared.com/q/1/iyengar Speaking from my own experience, pursuing Hatha Yoga is certainly worth the effort. Every session leaves me feeling calmer and more focused. It’s as if my body and mind immediately crave meditation or some other contemplative activity right afterward.
If you are looking for the highest return on investment regarding physical activity, I highly recommend the five Tibetan exercises. You can practice them alone or pair them with Hatha Yoga. Just make sure to track down the original 1946 version; most modern reprints are cluttered with nonsense or omit crucial instructions found in the source.
Ultimately, what is it you actually want to achieve through Yoga? What is your goal?