Not long ago an old friend asked me: "if you had to name the ten books that have had the most influence on you, what would they be?" (Really! He really did ask that.) Here's what I came up with after thinking about it for an evening. I find it interesting that so many of them (six!) were books I read after the end of my formal education.
The Demon-Haunted World: Science as a Candle in the Dark (Carl Sagan)
It is as valuable to understand the methods of science as the revelations of science, and to understand how and why they work.
Fear and Loathing in Las Vegas: A Savage Journey to the Heart of the American Dream (Hunter S. Thompson)
Showed me how prose could crack, pop, and whistle, and ensured I'd say yes to dropping acid the first chance I got.
The Grapes of Wrath (John Steinbeck)
The first Great American Novel that I read in high school, and evidence that conservative accusations of socialist indoctrination in public education might have a kernel of truth to them. It's hard (even for a sluggish goth kid in a gamer haze) to read Grapes of Wrath without experiencing sudden and serious misgivings about American capitalism.
History of the Peloponnesian War (Thucydides)
To quote a cartoon: "history is much like an endless waltz. The three beats of war, peace, and revolution continue on forever." From the recording of this particular strain that played out in Greece in the fifth century BCE, one can gain a fairly comprehensive understanding of the whole dance.
The Human Evasion (Celia Green)
"Astonishment is the only realistic emotion." If that's the case, human beings appear to be rather unrealistic. Why?
A Long Way from Euclid (Constance Reid)
My senior year precalculus teacher only passed me because she felt sorry for me. Since then I've managed to teach myself the basics of single-variable calculus and am currently working through a trig textbook. A Long Way from Euclid is the book that impelled me to revisit and explore mathematics for pleasure.
Miscellaneous Writings (HP Lovecraft)
Lessons learned: it's good to have hobbies, it's good to dabble in numerous fields of study and interest, it's good to stay in touch with friends, it's good to cultivate a consistent (and evolving) worldview, and it's good to write and keep writing.
Moby-Dick (Herman Melville)
I've said it before: this is the Third Testament. Beyond the Tanakh and the Gospels, there is the Whale.
The Wadsworth Anthology of Poetry (Jay Parini, ed.)*
I used to dislike poetry. (I had a real grudge towards Ginsberg, apparently.) This collection helped me to understand why that just wouldn't do.
War and Peace (Leo Tolstoy)
People, history, the world, life, everything, etc.
There you have it. HEY! Why don't you tell me the books that have influenced you the most?
* Yes, yes -- choosing an anthology is a copout. But I'm looking at Howl and Other Poems, Leaves of Grass, and The Collected Poems of William Carlos Williams, and none of them are nearly as bent and wrinkled from repeated reads as my copy of the Wadsworth Anthology.