Troy has the longest literary shadow of any archaeological site in the world; a few books make the visit immeasurably better.
Homer, The Iliad — the only essential one. The events the Iliad describes — fifty-one days in the tenth year of the Trojan War, around 1200 BC if any of it is historical at all — are the reason anyone has ever heard of Troy. Read the Robert Fagles or Emily Wilson translation on the bus from Çanakkale and the empty plain you cross from Tevfikiye becomes the plain where Achilles dragged Hector's body.
Caroline Alexander, The War That Killed Achilles (2009) — the clearest modern reading of what the Iliad is actually about: not glory but grief, not the war but its costs. Short and unpretentious. The perfect companion volume.
Michael Wood, In Search of the Trojan War (1985) — based on the BBC television series of the same name, this remains the best overview of the archaeology and the case for a historical Troy. Wood walks the site, interviews the archaeologists, and is honest about what the evidence does and does not support.
Heinrich Schliemann, Ilios (1881) — Schliemann's own breathless account of his early excavations is now a historical curiosity rather than a reliable source, but reading it on the site gives a vivid sense of the man whose enthusiasm — and whose destructiveness — produced modern Troy.
Madeline Miller, The Song of Achilles (2011) — a contemporary retelling of the Achilles story from the perspective of his lover Patroclus. Beautifully written, true to the spirit of the source material, and the best modern fiction set in the world of the Iliad.