It will depend on his interests really. My 10 year old daughter has really enjoyed listening to Bill Bryson's Short History of Nearly Everything. Is on her second go through in fact. She'e enjoyed The Hobbit, How to Train Your Dragon series, The Owls of Ga'Hoole, and some classics like The Jungle Book, The Snow Queen and Heidi.Also Journey to the River Sea by Eva Ibbotson (which is a great adventuring book alhtough initially with a female protagonist).
Ask your library what they can get in, if the current range doesn't appeal. We use Audible, which costs, but because she commutes quite a bit, it's been worth it.
Our library in Wellington allows audio books to be downloaded for borrowing. I haven't done it so can't tell you about the downsides/upsides. If you don't live in Wellington you may be able to become a member at some cost.
It's probably the same at Auckland library so it's worth checking their catalogue to see what they hold in their e-library.
From memory, and it's a while ago, I think it was something like $10 a year to join the Auckland library if you don't belong to the Auckland rate paying area.
Wellington library now have access to Tumble books for free. We have just discovered it and are watching the picture books while the audio plays. They have older books as well. With the library catalogs, Bolinda and Overdrive, you can limit the search to currently available books so they are instantly available. Your library may have something similar.