Into The Wild is great. Another great book by the same guy is Under The Banner Of Heaven, about some fundamentalist Mormon killers.
Confederancy of Dunces is one of the best books of all time. Great literature, easy to read, but with a lot to say.
Most Vonnegut is good, not all. Like Hemingway - try the Nick Adams short stories if you don't like the novels.
Schrodinger's Cat trilogy & it's predecessor trilogy Illuminatus.
Shakespeare. Nothing can beat Shakespeare when he's on his mark. Not saying this is an example of it, but I like it:
GLENDOWER
I can call spirits from the vasty deep.
HOTSPUR
Why, so can I, or so can any man;
But will they come when you do call for them?
GLENDOWER
Why, I can teach you, cousin, to command
The devil.
HOTSPUR
And I can teach thee, coz, to shame the devil
By telling truth: tell truth and shame the devil.