My list of most important nonfiction books.
In no particular order:
Manufacturing Consent by Edward Herman and Noam Chomsky
Contains a number of case studies where media bias is actually quantified. Explains the resulting (extreme rightwing) bias in a nonconspiratorial way.

Killing Hope by William Blum
The most comprehensive book about American Imperialism

Mad in America by Robert Whitaker
Simply being nice to the mentally ill works far better than drugs, lobotomies, electroshock therapies, drug induced seizures, diabetic induced comas, and many other barbaric "therapies". Furthermore the pharmaceutical industry lies about their patented drugs in order to maximize profits.

Bowling Alone by Robert Putnam
Quantifies a rather extreme increase in social isolation in America over the last century. Main culprits are the automobile, the TV and the internet.

Caffeine Blues by Stephen Cherniske
Caffeine is pervasive in our society and a lot more harmful than people realize. For some people even a cup of coffee a day has a wide range of harmful effects.

The China Study by Thomas Campbell
Meat, eggs and diary increases the risk of many diseases even in small quantities. The power of the companies which produce such products though has been highly influential in keeping this knowledge somewhat obscured.

I'd want to include a book about how one can be physically strong on a vegan diet. This link will have to suffice:
http://www.veganfitness.net/viewtopic.php?f=7&t=723&start=0

Anyway, these are some of the things I wish people knew a lot more about. Not that it matters. (Thank god/whoever).