I've seen a few DragonLance cosplayers, a couple of Discworld (I have one or two planned myself from that series) and... um, that's all I can think of right now.
If you do Aziraphale, you must have a Crowley.
A good idea is to pick a character who's widely recognizable for distinctive details-- a very notable outfit, unusual physical characteristics, etc. Or group them with other people so they're easier to identify: Violet Beaudelaire by herself (I'm not talking the movie version, here) might not get much notice, but if you have a Klaus and Sunny, and possibly a Count Olaf, then you're golden.
"And we are all told from the moment we open our eyes, that everyone is entitled to his or her opinion. Well, thatís horsepuckey, of course. We are not entitled to our opinions; we are entitled to our informed opinions. Without research, without background, without understanding, itís nothing. Itís just bibble-babble. Itís like a fart in a wind tunnel, folks." --Harlan Ellison