mmm... well for mind-stretching books i have a few to toss in...
One is an oldie and is sort of hippie is called Das Energi by Paul Williams. It reads a little like Lao Tsu... lots of bits of thought, some short, some long, on lots of topics... here's an example:
"If you could look infinitely far forward in time, if you could look infinitely far out in space, there is no question what you would see: You would see the back of your head."
Also, Fred Alan Wolf is quite interesting. I think i'd describe him as a metaphysical physicist... or maybe that should be shaman.
http://www.amazon.com/exec/obidos/se...001510-1371257
And i got sidetracked a while ago from a really good book called The Mind of God by Paul Davies. It's also a book that combines the new physics with questions about God and the spiritual make up of the world.
http://www.amazon.com/exec/obidos/tg...glance&s=books
I don't know yet what one book i would pick for myself yet, though. I've been thinking and thinking!