When I was in the seminary, Goswami Kriyananda gave us four books to read twelve times.  These spiritual texts contain the essence of eastern wisdom.  They are:

The Bhagavad Gita (The Song of God).  I own at least a dozen translations of this book.  I usually refer to Kriyananda's poetic and mystical translation or the Penguin Classics translation by Juan Mascaro.

The Upanishads -- Upanishad means 'sitting at the feet of the master' and it can also mean 'secret teaching' ie from guru to initiate.  Composed between 800 - 400 BC they offer commentary, expansion and development of the Vedas (the most ancient scriptures of the Hindus).  Again, I have lots of translations.  Juan Mascaro is again one of my references.  I also like Ten Principal Upanishads by Shri Pirohit Swami and W. B. Yeats which seems to be out of print.

Tao Te Ching by Lao Tzu -- this ancient Chinese philosophical text has many translators also.  I recommend reading several -- the more scholarly for background information and the newer ones (like Mitchell or LeGuin) for the poetry.  In the seminary, we read the Mentor edition translated by Blakely (but I can't find it on Amazon).  I've also read and enjoyed the translation by Jane English & Gia-Fu Feng.

Zen Flesh, Zen Bones A Collection of Zen and Pre-Zen Writings compiled by Paul Reps and Nyogen Senzaki.  Easy to read -- a lifetime of stories and koans to reflect on.

An introductory approach (and easier read) might be Gerald Jampolsky's books such as Love is Letting Go of Fear and Teach Only Love.

For the origins of the Course, read Journey Without Distance by Robert Skutch