It would be interesting to see what the best depictions are of specific characters in Batman's villain roster and take the time to explore them better. It could be a oneshot graphic novel, or an arc in the ongoing DC comics, or it doesn't have to be a comic at all. For The Joker a lot are probably going to say http://en.wikipedia.org/wiki/Batman:_The_Killing_Joke but there might be other great Joker stories out there. But what about the rest? Two-Face? Mr. Freeze? The Riddler? The Penguin? Hell, The Ventriloquist?