In the Heart of the Sea by Nathaniel Philbrick (2000) — The definitive account of the 1820 sinking of the whaleship Essex, stove by a sperm whale in the Pacific and the basis for Melville's Moby-Dick. Philbrick is a Nantucket resident and writes about the island's whaling history with real authority. Essential reading before any visit to the Whaling Museum.
Moby-Dick by Herman Melville (1851) — Melville's novel opens in New Bedford and Nantucket, and the Nantucket sections — the Spouter-Inn, the chapel, the departure from the harbor — repay attention knowing you're standing in the actual places. The whole novel benefits from knowing what Nantucket actually smelled and sounded like in the 1840s.
Away Off Shore by Nathaniel Philbrick (1994) — Philbrick's history of Nantucket from its settlement to the end of the whaling era. Less dramatic than In the Heart of the Sea but essential context for understanding why the island looks the way it does and why it still carries so much of its 19th-century character.
The Nantucket Diet Murders by Virginia Rich (1985) — A cozy mystery set on the island in winter, when the summer people have left and the year-round community closes ranks. Accurate in its portrayal of how the island changes when it isn't being performed for visitors.