School's out, or A scary magical adventure

Our last-day-of-school tradition involves a trip to the bookstore to sign up for the summer reading program (we signed up for the one at the public library already) and pick out a brand new book. This year Leo, who has always liked realistic fiction (think Andrew Clements), surprised me by wanting what he described as "scary magical adventure books." Scary? That didn't sound like Leo. It did, however, sound like some of his friends. Fortunately there were a lot of scary (but maybe not too scary) magical adventure books to choose from, and in no time he had acquired a tall stack and was inspecting them before deciding which one to buy. He decided on 100 Cupboards by N.D. Wilson, on the strength (I think) of its gorgeous green cover. He hasn't read it yet.

I wanted to show you a picture of the stack of books in question (so shiny!), but a bookseller politely informed me that photography was prohibited in the store. Company policy. To keep customers from buying the books online or checking them out of the library, maybe? I was mortified, apologetic, defensive, and finally understanding, if also unconvinced. Anyway, before I photograph the stack of scary magical adventure books we did check out of the library (ahem), please let me know what you would recommend in that genre, for an almost-9-year-old boy going on his very first one.

[Updated to add: Charlotte is looking for 70s-era fantasy books for a nine-year-old girl today.  I am partial to the 70s myself, having done some growing-up during them; and I think fantasy books cross over gender (and time) well.  Check out her recommendations!]