Well if your ever interested then Watchmen is my favorite graphic novel, if you haven't read it already. There's also a Batman story written by Alan Moore who's the same author called The Killing Joke (Which is what Heath Ledger used as his primary source material for The Dark Knight.) Marvel Civil War is a event series that was pretty good, and I'm sure you could just a paperback collection for cheaper than buying the comics individually.
There's also other Alan Moore books that I haven't read yet but plan on reading such as V For Vendetta, From Hell, The Lost Girls (A Lesbian "Porno" comic) League Of Extraordinary Gentlemen (Which is nothing like the movie if you've seen it: Mina Harker is the main character and it features a bunch of other literary characters like, John Carter, The Martians from War Of The Worlds, King Arthur and even James Bond)
Those are the main things that come to my mind right now, and if I think of anything else I'll let you know if you want.