Last weekend I stumbled onto an extraordinary introduction to architecture book, at a library used book sale:
Architecture: Form, Space and Order, by Francis D. K. Ching.
http://www.amazon.com/Architecture-Francis-D-K-Ching/dp/0471752169
This is a primer on the architect's though process-- the relationship of man-made structure in space. It is loaded with visual examples of classic structures from history, both ancient and modern, and from throughout the world, to illustrate each point. I just can't put it down. The illustrations and explanations are really good.
$3 was a good price. I see it goes for a lot more on Amazon.