in addition to lots of the above

Naked Lunch (Burroughs)
Nova Express (Burroughs)
Herzog (Saul Bellow)
Letters from the Earth (Twain)
A River Runs Through It and Other Stories (Norman Maclean)
Vietnam (Stanley Karnow)
A Religious Orgy in Tennessee (H. L. Mencken on the Scopes trial, some serious Americana)
any list of Great American Books has to include a collection of stories and poetry by Edgar Allan Poe
and, sure, i'll mention Huckleberry Finn again.