Lord of the Rings by JRR Tolkien still stands as one of my favorite books. Andrew Klavan has written some books I love like Werewolf Cop and True Crime. True Allegiance by Ben Shapiro is a great novel.
But I tend to like non-fiction books the best. Wealth of Nations by Adam Smith and the Federalist Papers by Hamilton, Madison, and John Jay are up there. Basic Economics and the Quest for Cosmic Justice by Thomas Sowell as well.