There's an Internet meme going around of "the books that most influenced me," usually in lists of 10, started by Tyler Cowen and furthered by Will Wilkinson, Bryan Caplan and Matthew Yglesias. Here's mine, in roughly chronological order.
1. Cosmos, by Carl Sagan. I read this around when it came out in 1980 (I was about 15) and never saw science as uninteresting again, even if some of my classes were. Enjoyed his intertwining of science and history; was less enthused by his politics.
2. Modern Times: The World from the Twenties to the Nineties, by Paul Johnson. Read this around the same time, and it furthered my conservative reaction against the 1970s. Later came to think of it as less than profound scholarship, but its sweep and drama still left an impression.
3. The Creation, by P.W. Atkins. An evocative view of cosmology, and as with Sagan, showed that science could be lyrical. Had some affinity for Atkins' atheism, but remained wary of dogma in matters of religion (or non-religion).
4. Safire's Washington, by William Safire. Safire's brand of libertarian conservatism always appealed to me. Still does, perhaps because he managed to avoid either libertarian or conservative extremes.
5. The New Left: The Anti-Industrial Revolution, by Ayn Rand. I was never really a Randian, but I was definitely fascinated by her while in college and at times thereafter. Unlike many, I didn't start with her novels, and never liked them. But the non-fiction essays in this book, particularly "Apollo and Dionysus," drew connections for me between politics and science.
6. The Rise of Theodore Roosevelt, by Edmund Morris. A rousing story about a great man en route to the presidency. I could never buy into the later right-wing disdain for T.R.
7. The Last Lion: Winston Spencer Churchill, Visions of Glory and The Last Lion: Winston Spencer Churchill, Alone 1932-1940, by William Manchester. These fostered my sense of history, fascination with greatness, and loathing for appeasement and pacifism as causes of war.
8. The History of the Decline and Fall of the Roman Empire, by Edward Gibbon. An epic story, presented in a formal yet accessible writing style that influenced, among others, Churchill (and me).
9. The Case for Mars: The Plan to Settle the Red Planet and Why We Must, by Robert Zubrin. This expanded my affinity for space exploration, helping make that the main focus of my career for a few years around the late 1990s. I never was sure we need a crash effort to get to Mars, though, and have become less enthused about that over time.
10. Alexander Hamilton, by Ron Chernow. He was incredibly smart, and right about a lot of things; and as with T.R., I have little interest in libertarian dismissals of him. This book helped inspire my turn toward writing on economic and financial history in recent years.
11. Bonus book: Science: Good, Bad, and Bogus, by Martin Gardner. Hilarious as well as thought-provoking.
Buy any of these books via the Amazon links above and I'll potentially get some share of proceeds. (As is true with Amazon links throughout this site, though proceeds have been scarce.) Note: I've generally tried to link to the versions of the books I read, not later revisions.