I'd add The Comedians to the Greene list.
Travel books & other eye-witness accounts, perhaps, for varied perspectives. Perhaps Travels in Arabia Deserta, by Charles Doughty, The Silk Road, by Sven Hedin (his fascism doesn't colour it too much), & In Patagonia, by Bruce Chatwin, for a bit of fiction mixed in (as with Paul Theroux's travelogues). I'd definitely recommend The Conquest of New Spain, by Bernal Diaz - who was there.
I recall that The Prince was on every would-be-intellectual teenager's reading list when I was one.
I also liked The Evolution Man, by Roy Lewis.
Looking over my bookshelves for more varied perspectives, what about The Interpreters (Wole Soyinka), Diary of a Mad Old Man (Junichiro Tanizaki), Kill Me Quick (Meja Mwangi), Silence (Shusaku Endo) A Woman in Berlin, or A Diary of the Plague Year (Defoe)?