Several people have already suggest traditional photography books that I would have recommended so I'll offer something out of left field: "An Anthropologist on Mars" by Oliver Sacks
The famous neurologist presents a collection of essays, many of them dealing with sight and visual perception. This book will really make you *think* about what you see and why. It's fascinating and thought provoking, but also enjoyable just to read for the pleasure of Dr. Sacks' down-to-earth prose and obviously warm feelings for his patients.
