(Hermes Trismegistus)

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As above, so below... I realize not everyone has a personal library of Gnostic/Neoplatonic/Hermetic literature... Well, maybe it's time you started your collection.  (The Western esoteric tradition is older, weirder and remarkably more similar to to Eastern mysticism than you probably think.)

If you could only have one book from this section of my library, make it Gary Lachman's staggeringly comprehensive (and immensely readable) history The Secret Teachers of the Western World.  For a great spiritual guidebook that manages to please secular folks, nondualists, Zen types, and agnostics while still lending support to the world religions, take a look at The Wisdom of Hypatia, by Bruce MacLennon.  It's a quick-study on NeoPlatonism, and an inspiring how-to philosophy for happiness.  For a controversial (but utterly beautiful) take on Christianity, read Tom Harpur's The Pagan Christ.

But you can't go wrong with any of these books.