Adam Smith's " An Inquiry into the Nature and Causes of the Wealth of Nations" or just "The Wealth of Nations" could be really useful in an argument if you haven't read it. Marx's "Das Kapital" as well. Though I have a feeling you've at the very least perused both of those.
Alex Ross' "The Rest is Noise: Listening to the Twentieth Century" has been recommended to me several times. Charles Ives' "Essay Before a Sonata" is a good read, especially if you have listened to or are interested in his Concord Sonata (Don't ask me why I love this piece. I haven't figured out yet).