Just finished "Understanding Comics" by Scott McCloud. It was on the must read list by the Whitman College Art Department. I found the book fun to read (it is done in comic book format) and very informative. McCloud does a really good break down of how humans deal with visual language. The book was written in 1993 so the book has a "Hey Comics are a legitimate art form, Dammit!" I think 17 years later comics have received more recognition and are no longer the redheaded step child of the art world.
http://www.powells.com/biblio/1-9780060976255-0