If you want something recent, I’d go for Richard Russo’s Nobody’s Fool — to my mind, the best novel by an American in the past 20 years. If you want something half a century old, I’d go for Seize the Day by Saul Bellow or Shadows on the Hudson by Isaac Bashevis Singer. If you want something 80 years old, I’d go for The Great Gatsby. If you want something 100 years old, I’d go for The House of Mirth by Edith Wharton. Older than that? The Rise of Silas Lapham by William Dean Howells, Washington Square by Henry James and, of course, Huckleberry Finn.