Books for the kid "who just wants to read Harry Potter"

Believe it or not, this is the question that got me into serious book reviewing, about 15 years ago: 

"My son loves Harry Potter, but he won't read anything else! What are some books you'd recommend that would be exciting enough to tempt him to start another story?"

My answer then was the same one I still give first nowadays:

Artemis Fowl, by Eoin Colfer.
The action, the humor, the sci-fi "magical" world…all of it is sure to draw in the most reluctant readers. That reader I mentioned above? He dove into Book 1 and never stopped raiding his library shelves for more and more books. It took just a few months for him to consider himself an obsessive reader.

I've added a few more ideas to my list since then… Many are series (because after a series you love, it can sometimes be hard to jump into a number of standalone books in a row). Almost all are humorous and adventurous and gripping. And they're all excellent on audio as well!

Artemis Fowl series, by Eoin Colfer
The False Prince series, by Jennifer Nielsen
Roald Dahl's children's books
Chitty Chitty Bang Bang, by Ian Fleming; and the new sequels by Frank Cottrell Boyce (Of all the books on this list, Chitty Chitty Bang Bang almost didn't make the cut, even though I love it. But the sequels are so fast-paced and constantly laugh-out-loud funny that I had to include them! You could always watch the movie and then skip ahead if your kids aren't ready for the slightly more slow and challenging style of the original.)
Sputnik's Guide to Life on Earth, by Frank Cottrell Boyce (the audiobook's narrator is Peter Capaldi—of Doctor Who—and he does an amazing job)
Cosmic, by Frank Cottrell Boyce
Beneath the Swirling Sky, by Carolyn Lieloglou (this is the first in a series; the second will be released this fall)
Holes, by Louis Sachar
Echo, by Pam Munoz Ryan (especially wonderful on audio!)
The Incorrigible Children of Ashton Place series, by Maryrose Wood (another audio book par excellence.)
Redwall series, by Brian Jacques
Peter and the Starcatchers series, by Dave Barry and Ridley Pearson
Tuesdays at the Castle series, by Jessica Day George
The Girl Who Drank the Moon, by Kelly Barnhill (slightly on the mature side, so check it out before handing to a younger child)

What books would you add to the list?