Three? Not five? Or even ten? I can't do three. Oh boy. I'm assuming you don't mean SK books exclusively. But all books. For me, The Great Gatsby will always be #1. I take that back. There have been brilliant books written since then and one might certainly, in my lifetime, overcome it. Second I'd probably put
Fitzgerald's Tender is the Night. Do you see a pattern forming here?
I'd probably put Hemingway's
Movable Feast in there, Vonnegut's Slaughter House-Five, Don Quixote, Maybe
Under The Volcano by Malcolm Lowry. Harlan Ellison's
I Have No Mouth, and I Must Scream? Cormac McCarthy's
Blood Meridian? I think I've gone past 5. If I was going to do three SK books I'd say:
Duma Key, Salem's Lot, and The Stand.