Ireland has one of the richest literary traditions of any small country, and reading some of it before you go adds considerably to the experience.
Fiction and literature
Ulysses by James Joyce (1922) — the most famous Irish novel, and one of the most famous novels in the English language. It is set over a single day in Dublin (16 June 1904). Difficult but rewarding; Dubliners, also by Joyce, is a better starting point if you haven't read him before.
The Remains of the Day author Kazuo Ishiguro wrote The Unconsoled — but for Ireland specifically, the collected stories of William Trevor (The Collected Stories) are extraordinary: quiet, devastating accounts of Irish provincial life across the 20th century.
Amongst Women by John McGahern (1990) — a novel about a domineering IRA veteran and his family in rural County Leitrim. Compact and powerful.
The Gathering by Anne Enright (2007, Booker Prize winner) — a Dublin family returns after a death. One of the best Irish novels of the 21st century.
Normal People and Conversations with Friends by Sally Rooney — contemporary Dublin and the west of Ireland, sharp and widely read.
History and non-fiction
How the Irish Saved Civilization by Thomas Cahill (1995) — isbn: 0385418493 — a popular history of how Irish monasteries preserved classical learning during the early medieval period. Slightly oversells its thesis but genuinely engaging.
1916: A Novel of the Irish Rebellion by Morgan Llywelyn — isbn: 0812574923 — fictionalised account of the Easter Rising.
The Great Hunger by Cecil Woodham-Smith — the definitive account of the 1845–52 famine. Harrowing and essential for understanding modern Ireland.
Travel and background
McCarthy's Bar by Pete McCarthy — a British writer travels through Ireland in search of pubs called McCarthy's. Funny and affectionate.
Paddy Clarke Ha Ha Ha by Roddy Doyle (1993, Booker Prize) — childhood in a Dublin suburb in the 1960s, told entirely from a child's perspective.