Douglas Adams, Terry Pratchett, Mark Twain, and Robert Heinlein are obvious ones for me, as is Carl Sagan, and Stephen Hawking
I have a few e-books on my iPhone that I’ve been getting around to reading as well, a few P.G. Wodehouse novels, some Confucius, Kafka’s Metamorphosis, Plato’s Republic, and Darwin’s Origin of Species
C.S. Lewis, Charles Williams, and Dante – C.S. Lewis was my first introduction to someone thinking intelligently about Christianity (though he’s got his own blind spots, to be sure), and the latter two subtly but surely influenced a lot about my personal theology.
And I remember Susan Cooper’s Dark is Rising books being my first introduction to a thoroughly non-Christian worldview, which definitely also had a strong influence on my thinking.
Oh! And, this is totally random, but there were these fantasy books, the Time Master trilogy, by Louise Cooper, that had this kind of… I don’t know… Manichean? worldview where good and evil/light and darkness had to be in balance, that had a huge impact on the way I thought in middle school, though later I decided it was a little silly.
And Tolkien. Probably in lots of ways; one random but important way is that it is directly due to him that I’m against the death penalty (“Many that live deserve death. And some that die deserve life. Can you give it to them? Then do not be too eager to deal out death in judgment. For even the very wise cannot see all ends.”)
And Heinlein and Rand, like everyone else.
And, on the nonfiction side, Richard Feynman’s Surely You’re Joking colors a lot of how I think and feel about science.
Harper Lee’s To Kill a Mockingbird
Atticus Finch taught me the definition of character and integrity
Robert Heinlein had an influence on me at an early age: he got me interested in science with Have Space Suit, Will Travel.
Carl Sagan and Richard Dawkins had an influence on me as a young adult.
Leon Uris for Trinity
Colette (no particular translator) her non-fiction especially
Hans Christian Anderson
Longfellow (when I was 12-13) for the poems “Evangeline” and “The Wreck of the Hesperus”
Johanna Spyri for Heidi
Louisa Mae Alcott (as a child and adolescent)
Henry David Thoreau
Ralph Waldo Emerson
(You can bet that I love Concord, MA)
S. I. Hayakawa
John Ciardi
Tom Brown for The Tracker
W.B. Yeats
Ray Bradbury - for a short story about a fog horn and a poem about a tree
Thomas (not Tom) Wolfe - for Look Homeward Angel
Gloria Steinem
Ernest Hemingway’s non-fiction
Beverly P. St. John
King David
Hudson ? – the author of Green Mansions