The Olympians (Greek God graphic novels) by George O'Connor.
Bone (graphic novel series) by Jeff Smith
Monsters Beware and Dragons Beware by Jorge Aguirre
13-Story Treehouse (and 26-story and 39-story sequels) by Andy Griffith.
There are also graphic novels of some of the Percy Jackson books, but those books are so good I would hold out for your son to read them in original form. They'd be a good foundation for the other end of your bridge to fiction. They (along with Magic the Gathering cards) were really the reason DS7 "decided" to learn to read.
