Upworthy has an exhaustive (but not at all exhausting) list of young-adult books besides the Harry Potter series for the teenager in your life (or you—no judgment!).
Historical fiction (The Book Thief, Island of the Blue Dolphins), utopian/dystopian fiction (The Giver, The House of the Scorpion), classics (Charlotte’s Web, Where the Red Fern Grows)—it’s all there.
In fact, even Harry Potter is on there, just, you know, for completeness’s sake.