Diana Wynne Jones. Now, I don't want to say anything bad about dear old Harry, in fear of being deluged with hate mail. So, a disclaimer: I *liked* Harry Potter. Well, moderately. I don't think Harry Potter is a god or anything. After reading The Sorcerer's Stone, I thought "There has got to be more than this", and so I went out to find Diana Wynne Jones' Chrestomanci series.
Now I've read two of them: Charmed Life, and Witch Week. Both books surpass Harry in depth of character (etc.) and in quality of writing, but Witch Week is the better of the two. The plot is intriguing: in a world exactly like ours, except that they still burn people as witches, someone in a sixth-grade class is accused of being a witch. It sounds pretty serious for a children's book, but Diana Wynne Jones treats her subject with sensitivity and humor. (Some parts are actually hilariously funny.) By the end, all the questions you had are answered, and everything is resolved in an unexpected but satisfactory way that only Diana Wynne Jones could pull off. Overall, an excellent book.
If you think Harry Potter is the center of the universe--excuse me (don't insult anyone), let's start over, If you liked the Harry Potter books, you must try Diana Wynne Jones. If you're really devoted to Harry Potter, you'll probably never allow another book to take its place. But keep an open mind, and try to see that there are more great books out there.