Terry Southern, especially 'The Magic Christian.' Made into an awful movie adaptation with Peter Sellers and Ringo Starr.
'Magic Christian' is a seminal work in transgressive fiction, yet I'm surprised how many people who love Edward Abbey, Irvine Welsh, Chuck Palahniuk, Kurt Vonnegut, etc., have never even heard of Terry Southern.
Some other books that don't get enough consideration:
Orwell's 'unfamous' work. 'Homage to Catalonia,' 'Wigan Pier,' and 'Down and Out in Paris and London' all provide important insights into both the conditions of the Spanish Civil War, the plight of coal miners in Northern England and vagabonds in the Depression, but also shed a lot of light on the scandalous behavior of the Stalin regime and its puppets. What makes Orwell so great in these books is he is trying to function as a watchdog FOR the left. While he may have been misguided, he was very capable of critical thinking. And 'Animal Farm' and '1984' the two everyone's heard of and/or read make much more sense if you read those three. I'm not as big on 'Burmese Days' or 'Keep the Aspidistra Flying,' though 'Down and Out' and 'Wigan Pier' certainly let you in on where 'Aspidistra' came from.
Also, Thomas Harris is mainly known for the serial killer books, but 'Black Sunday,' his first, is worth a look. I'm surprised it hasn't enjoyed a revival in the post 9/11 era, both because Harris has enjoyed so much commercial success with his other books, and the fact that he saw it coming so accurately, 30 or so years ahead of time...
