Alice in Sunderland: its sorta a novel slash documentary, describing the history of a surprisingly interesting city.
Red Son: What if Superman was a Soviet, and our only hope was a genius called Lex Luthor?
Corto Maltese: Tin Tin for grown ups, about a globe trotting sailor who fights, shags and recites poetry through the early 20th Century.
Note that strictly speaking, none of these are really graphic novels, but also strictly speaking, I hate how people try to distinguish their big-boy-grown-up-comics from normal comics.