- The Bhagavad Gita, by a certain hindu wise man, or several of them (albeit you will probably need a commentary for this one, since it's complex and may be uncomprehensible for you - on that, check the "ANUS book list" topic)
Eh, I would definitely stay away form the Gita, I mean sure it's a classic but so is The Bible, should we recommend Marcus that too?
For classics I would recommend:
A Brief History of Time by Stephen Hawking - explains all sorts of science things like quantum physics and general relativity and it doesn't throw any equations at you (you can be science-illiterate and still understand it perfectly)
Tao Te Ching by Lao Tze - one of the perennial Taoist works
The Holographic Universe by Michael Talbot - this is more of an underground classic, takes scientific theory and experiment (from Bohr, etc) and combines it with modern spirituality
some book by Alan Watts - I'd recommend The Wisdom of Insecurity by Watts; Watts was a classic of his time and the first to bring Eastern spirituality to the West
some book from the Carlos Castaneda series - I prefer the earlier writings up until The Power of Silence; a classic series discussing spirituality, left-hand-path paradigm, shamanism, etc
the Mulamadhyamakakarika by Nagarjuna - really dense writing but you could read a summary instead; one of the perennial Buddhist works
The Medium is the Massage by Marshall McLuhan - a short book with clever pictures, really busts mainstream memes and offers a nice look into the leading edge of thought of that time period
some books by Carl Jung - definitely read Jung over Freud!; I recommend The Undiscovered Self or a posthumous collection of works with a bit of new material too called Memories, Dreams, Reflections