Pride and Prejudice (Austen) and
Rape of the Fair Country (Alexander Cordell) contrast and complement each other rather well, showing opposite ends of 19th century society - the harsh, deadly reality of industrialisation without which the refined world of manners would not have been able to exist.
Into the Silence (Wade Davies) - a non-fiction account of the impact of World War One and the subsequent attempts to climb Everest in the early 1920s. A beautifully drawn essay (OK, a very long essay) on the long-term tragedy of war, with amazingly thorough research.
Ulysses (Joyce) - that would be my Desert Island book. You can open it at any point and start reading (preferably out loud) and just delight in the sheer pleasure of language.
Buddenbrooks (Thomas Mann). An amazing study of decline and fall at the family level - but also ultimately the end of empire.