My son has read many of what your son has. Great little minds think alike!
There is a new Rick Riordan book out -- Magnus Chase. Norse gods for that new series. Also try the Red Pyramid series by him if you haven't already.
Little dude has read many Brandon Mull series, including ones you listed. He also liked the Beyonders.
Our school librarian suggested the Ranger's Apprentice series, which he comes home with books from pretty often. Also a fave are the Spirit Animal books, the Dragonet serieses (there are two, he told me), Septimus Heap (7 of Septimus, 2 now of TodHunter Moon), and also relatively new is Iron Trial/Copper Gauntlet from Cassandra Clare and another author about a magic school, so kind of like HP, but not.
He's also read James Dashner. He's read 2 of the Morality Doctrine books thus far. The next comes out mid-November. He's already told me, LOL!
He also loved the Seven Wonders series,
Hope this helps! It can be a challenge to keep up with them!
