Art Spiegelman's Maus has a straightforwardness to it that makes it look easy, but the book MetaMaus: A Look Inside a Modern Classic is testimony to the years of preparation that went into the book. MetaMaus includes a lengthy interview with Spiegelman on his sources, his process, and the research he put into Maus, as well as illustration of primary source material and lots of sketches. The book is accompanied by a DVD that includes both volumes of Maus and audio recordings of Spiegelman's father Vladek, who narrates the story to his son.
Suvudu has posted a 24-page excerpt from the MetaMaus DVD that shows the preliminary sketches and finished pages of two pages of Maus, and it's well worth a look to see how Spiegelman developed his story on paper. The book complements this nicely with Spiegelman's descriptions of the work, and it's well worth checking out when it is released on Oct. 4.