Reddit mentions of Raja-Yoga

http://www.amazon.com/gp/aw/d/091120623X/ref=mp_s_a_1_1?qid=1394128027&sr=1-1

Autobiography of a Yogi by Paramahansa Yogananda, it blew my mind and totally changed my life. The yoga techniques the author teaches taught me how to access the peace and joy available in deep meditation.

Bhagavad Gita (translated by Eknath Easwaran, it's a really beautiful translation, much better than the others IMO)

I'd have to think for a while to try to come up with another book that had the effect on me those two had.

Raja Yoga by Vivekananda also is a deep and powerful book.

Edit: added links for the books, added third book.

Right now I'm reading Swami Vivekananda's transliteration of the yoga sutras and I highly recommend it. He wrote his version of the translation over 100+yrs ago and I'm fascinated by the way he worded things because they feel so relevant to today. 'Relevant' even beyond the fact the yoga sutras are a "How to Human" guide, Vivekananda spent time in Europe studying Western philosophy and in his introduction he very effectively lays out the differences between the logic systems of Western philosophy and Yogic philosophy as described in the sutras.

It's in Google Books for $.99 as "The Yoga Sutras of Patanjali" but from what I've seen in the Amazon comments, this version is an excerpt from a book he wrote called Raja Yoga (link to it on Amazon) where he translates the sutras and then also talks further about Raja yoga.