Zen and the Art of Motorcycle Maintenance is a good shout. The Pearl - Steinbeck The Gods Themselves - Asimov Also, George Orwell isn't American, he's English
The Adventures of Huckleberry Finn The quintessential American book by the quintessential American author
See, I was going to say that, too. But then I was like, "This is Sam Spade..." and I figured it's probably a profound statement. I'm still working on its meaning.
Hemingway is nice. More social commentary, but politics are often the backdrop for the social commentary. For whom the bell tolls, A farewell to arms, men without women.
If you're into philosophy, you might look into Henry David Thoreau, Henry James or Nathaniel Hawthorne. All excellent American authors that are sure to win you brownie points with any teacher or professor. Or, if you wanna go more modern with it, Phillip K. Dick (definitely will be able to work in some governmental themes with him as well) or Kurt Vonnegut. They will obliterate your reality.