Here's some more to add to your list:
"Two Little Savages" E.T. Seton--Adventures of two boys living as Indians; explaining Indian ways, woodlore, pioneer methods.
He's at the right age for Robert Lious Stevenson, but I don't know his reading level.
Same thing for Rudyard Kipling. Great books for boys.
E.Nesbit's books, esp. The Book Of Dragons--Eight madcap tales of unpredictable dragons — including one made of ... and excitement for make-believers of all ages.
"The Wind in the Willows" is a hoot. Any of the Kenneth Grahame books are good.
Robin Hood-Howard Pyle's version
Sir Arthur Legends
If you don't like the magical elements of "Arthur", their is a substitute called
"The Terrestria Chronicles". It's an allegory, knights type tale.
Also, he's at the right age for the Narnia Series and "The Hobbit". The HObbit is easy to read, not like The Lord of The Rings!
He might enjoy going through The Boy Scout Manual from 1911 or 1908.
YOu may also consider the 2-series by Douglous Bond of Vision Forum, the first is:
The Crown and Covenant
and the sequels of:
The Faith and Freedom series
They can be purchased individually, maybve even from Christinbook for less.
At Yesterday's Classics there is are many great books to choose from in his age bracket. Look in the Legends area:
and the History:
The "Our Little...Cousin..." series looks really good. And their are some high quality abridged versions of several books. James Baldwin did excellent abridgements, and I usually shy away from those.
Lastly aer audiobooks. Like you said they are great ways to get a book book in or introduce him. I think Jim Weis does the best dramatizations. He has several classics, inc. Mark Twain that your son may enjoy. My son really enjoyed "20,000 leagues under the sea". There are many to choose from inc. dramatizations of the Henty books, instead of straight readings.
For straight readings (from someone with a great voice) and other book choices go to Jim HOdges.
Many of these books can be found at your library of interlibrary. Amazon has excellent used copies, of even the Weiss stories (that's where I've gotten ours).
Hope this helps,