
Well, this seems like it's all over the serious blogosphere (hat-tip to Ta-Nehisi Coates), so I might as well try my hand at it.
1) The Lord of the Rings -- created both a love of fantasy and has intimidated me into not writing for many years. I'm slowly coming to a realization that no, I don't have to be building my own languages a la Tolkien in order to be a good fantasy writer.
2) Narnia -- escaping into other worlds, of course, and the idea that God may present in different faces/aspects at different times. However, as I get older, I realize how limited and how Calvinist Lewis's vision was.
3) Revolt in 2100 -- If I were setting national curriculum for the entire United States, I would make this required reading for every single school child, from first grade or so on up. This shows the danger of fundamentalism/the Dominionists.
4) The Women's Decameron -- I got my hands on this one in about fourth grade IIRC. I loved the community the women on the hospital ward developed. The section on adultery convinced me that cheating simply isn't worth it, and was part of what saved me from a player when I was in college.
5) Broca's Brain -- introduced me to the joy of reading about science, the process of discovery, and the sheer fun of finding out how things work.
6) Isaac Asimov's Robot stories -- good insofar as you had robots and Susan Calvin as the mad leet roboticist. Bad insofar as Susan Calvin was depicted as an emotionless freak.
7) The Naked Ape -- the other thing that saved me from a player when I was in college. "If he talks to you, he will talk about you" FTW.
8) Terry Pratchett (particularly Men At Arms, Small Gods, and Granny Weatherwax) -- Cheery Littlebottom showing the female scientist who's had it with trying to fit in with a male-dominated system. Small Gods as the Enlightenment and Vatican II rolled into one. Granny Weatherwax for saying that the fundamental sin comes from treating people as things.
9) Lois McMaster Bujold (particularly Mirror Dance and Memory) -- going on even after disaster happens. How societies react to the disabled.
10) Eric Flint (1632verse, Belisarius) -- 1632verse for how to create a country and legal system; Belisarius for the sheer fun of having a crystalline intelligence learn what it is to be human, and for the freedom/free will trumping predestination/tyranny theme.
Honorable Mention
11) Jane Austen's Persuasion -- I love the theme of "second chance at love"
12) The Divine Comedy -- I first got my hands on this one in fourth grade. Most of it went over my head at the time. I was much more busy reading the footnotes to try to figure out just who all these people were and why Dante was putting them into Hell. What I did take away was that even popes and priests could go to Hell, despite how the official history tried to spin things.
13) Andrew Greeley -- one of the people who's kept me identifying as Catholic for as long as I have. If I were dictator of the Universe, I'd make him Pope. (Not that he would particularly appreciate this, particularly w/ his current health)
14) Spider Robinson -- hopeful SF, lapsed Catholic, practicing Zen Buddhist.
15) Diane Duane (both the Wizardry series and her Star Trek books) -- joy in creation and the creative process. And yes, I am a sucker for the Good vs. Evil conflict.
Interesting that the vast majority of this is fiction, and specifically, science fiction/fantasy.