My DS7 loved the Familiars series. I think it's a bit easier than Harry Potter, but he loved those books. He's currently enjoying the 39 Clues series.
For more challenging books, I would recommend Half Magic. I think the lexile is a bit higher. Matilda by Roald Dahl is a favorite. You might consider A Wrinkle in Time or the Chronicles of Narnia for more classic books.