Here is a list of four books that radically changed the way I think about things.
On Aggression by Konrad Lorenz. This book was published in English in 1966 (having previously been published in German). This book is pretty much about how the study of animal behavior can be transferred to the study of human behavior, particularly in the way it shows aggression to be a natural response. How is it that two dogs can fight and one can be perfectly capable of killing another, yet refrain from doing so? This book has so much truth in it that I would like to see it be required reading for high school or college students.
This book forever changed the way I look at human conflict.
Microcosmos by Lynn Margulis and Dorion Sagan This book was controversial when it was published. Some of its conclusions have become mainstream while others remain controversial, and its style has been criticized. Still, it changed the way I look at micro-organisms and life in general. The idea that chloroplasts and mitochondria originated as free-living organisms, symbiotic with the organisms that became eukaryotic was revolutionary at the time.
The Mismeasure of Man by Stephen Jay Gould was about how science carries its prejudices with it, and can be used to give legitimacy to conclusions that are not really supported by the facts.
Bumblebee Economics by Bernd Heinrich. This book explored thermoregulation in insects, but really showed how science can be fun. In fact, I would recommend any book by this author.
Just putting the list out there. Recommended reading to anyone.