Three Thieves Series - All ages adventure/comedy series by Canadian cartoonist Scott Chantler.
Bone - All ages adventure/fantasy/comedy series. Epic.
Toon Books! - Comics by some of the best cartoonists working today, written for very early readers.
Star Wars Jedi Academy Series - All ages stories set in the Star Wars universe by Jeffery Brown.
Princeless - All ages fantasy with a strong female lead.
Smurf Series - Great for expanding vocabulary through context. Readers have to smurf what they are actually saying.
Recommended Books for Comics Education
Let's Draw Some Comics! A Guide for New Cartoonists by Matt Smith!