Newsweek has an article on how graphic novels have become mainstream. Should've appeared much, much earlier, in my opinion - Persepolis and Jimmy Corrigan have been major novels for a while already.
Since the article mentions the major American artists - Art Spiegelman (Maus), Daniel Clowes (Ghost World), Alan Moore (The League of Extraordinary Gentlemen) - might I recommend the understated work of the Brit Raymond Briggs? When the Wind Blows is perhaps one of the sweetest, saddest graphic novels I've seen on the topic of coming to grips with nuclear catastrophe. And Ethel & Ernest shows just how powerful nuanced personal history can be as a means of describing social history.