I would suggest that you use some of the classic literature with this child. Tom Sawyer is a good example. There's plenty of action, yet the characters are children and act like children. There is also plenty to discuss as the language is challenging and the plot has some unexpected twists. You could even introduce literary devices to this student if he is interested. Have him find examples of irony, foreshadowing or metaphors in what he reads.
Other books that might be appropriate for an eight year old:
The Witch of Blackbird Pond
Call of the Wild
The Wind in the Willows
The Chronicles of Narnia
A Wrinkle in Time (one of my all-time favorites and I read it first at age 9)
I bet others will be able to add to this list. The trick, I think, is to think of books where the ideas are multi-leveled and the reading level is fairly high. This way he can understand the book at a level where he is comfortable and still be challenged by the reading.