That was the very first book I ever bought. It was at the school book fair.

I'll take a stab at it.

The Complete Works of Thomas Paine.
The Federalist Papers (I realize it's not really a book, but still...)
The Holy Bible.
The Count of Monte Cristo. (Vengeance is not always a good thing. Plus so many other human emotions explored. Read the unabridged version).
The Brothers Karamzov.
Band of Brothers (So much to learn about good and bad leadership in this book, plus it is just a good read).
The Odyssey.
To Kill a Mockingbird.
Catch-22 (Because, well, I don't know I just like it. And you can't see it because you have flies in your eyes if you didn't).
Death Be Not Proud. Somewhat a child's read, but it shows how to live and die.

Some of these have been listed already, but here's a small list of "required reading" imo:

1. The Bible (Most printed book in human history, foundational text in western society)

2. The God Delusion by Richard Dawkins (Counterpoint to the Bible, argument for non-religious world view)

3. The Rights of Man, and other writings, by Thomas Paine (important for understanding the revolutionary period in France/US)

4. Road to Serfdom by F.A. Hayek (great discussion on political philosophy, collectivism vs liberty)

5. Democracy in America by Alexis De Tocqueville (mid 19th century review of America's political evolution, very influential)

6. 1776 by David McCullough (or anything by him for that matter, his biography on John Adams was very good)

7. Guns, Germs, and Steel by Jared Diamond (won the Pulitzer prize, history of the rise of society/culture through proximity to resources, very interesting read)

8. Plato's Republic (may be the cornerstone of western philosophical thought)

9. The Divine Comedy (Inferno) by Dante Alighieri (a true classic)

10. Shakespeare (King Lear, Hamlet, Macbeth, etc.)