A few months ago I started writing a post called "Top Ten Books that Changed My Life": when I started searching for similar lists by other readers, I stumbled upon the Broke and Bookish's 'Top Ten Tuesdays' game. I have never posted my list, because my explanations of how the books influenced my thinking were altogether lengthy.
I'd like to answer BTT's query, though, so I'm going to post the list but minimize elaboration.
1. Guns, Germs, and Steel. Jared Diamond (2004 or 2005)
Contribution: One, it made me realize that nothing happens in a vacuum, that history is best understood when supplemented by other disciplines (geography, politics, sociology). Two, it forced me to consider how human history is influenced by matters beyond human control.
2. Shadows of Forgotten Ancestors, Carl Sagan (2006)
Contribution: Led to my embracing the naturalistic worldview.
3. Universe on a T-Shirt, Dan Falk (Summer 2007)
Contribution: Made me realize that science was a search for meaning and understanding, not just a collection of facts.
4. The Meditations, Marcus Aurelius (Thanksgiving 2007)
Contribution: Introduced me to Stoicism and impressed upon me the advantages of mindfulness and a philosophical life.
5. The Communist Manifesto, Karl Marx (Summer 2008)
Contribution: The Manifesto is not a political blueprint, but a work of historical and social criticism in which Marx presents a view of history as being not just influenced by, but solely driven, by economics. While it didn't make me stand up and start preaching about the Historical Dialectic, after reading Marx I never thought about politics or the media the same way again.
6. Technopoly, Neil Postman (Summer 2008)
Contribution: Made me realize that the use of technology carries with it values: for instance, the ubiquity of wireless communication allows everyone to be "connected" virtually all of the time, and brings with it the assumption that this being connected is normal and good.
7. Amusing Ourselves to Death, Neil Postman (Winter 2008/2009)
Contribution: Postman believes that technologies change the way we interact with the world, and that electronic media enforces triviality by treating information as entertainment. Much of the book examines television with a critical eye, condemning it for reducing intellectual discussion and debate to talking points and put-downs
8. A Life of Her Own, Emile Carles (Spring 2009)
Contribution: Carles expanded my political horizons significantly. Before reading her biography, I thought of socialism and communism in terms of Big States like the Soviet Union and China. I never realized there was a strong, vital democratic spirit in these movements, and that anarchism and libertarianism were not far removed from them.
9. The Zinn Reader, Howard Zinn (Fall 2009)
Contribution: Zinn changed the way I thought about democracy. I once thought being a good citizen meant voting and such, but Zinn and Thoreau taught me that democracy meant action. Democracy is the labor strike, the slave revolt, the protest march: it is people taking control of their lives, not casting votes for 'represenatives' whom they do not know and have no business trusting.
10. Red Emma Speaks, Emma Goldman (Spring 2010)
Contribution: Goldman's philosophy of anarchism brought together many various threads of my intellectual and personal life, best summarized in this quotation:
"Anarchism, then, really stands for the liberation of the human mind from the dominion of religion; the liberation of the human body from the dominion of property; liberation from the shackles and restraint of government. Anarchism stands for a social order based on the free grouping of individuals for the purpose of producing real social wealth; an order that will guarantee to every human being free access to the earth and full enjoyment of the necessities of life, according to individual desires, tastes, and inclinations."