Videogamedunkey, famous for coining the phrase "It really makes you FEEL like Batman," did a list of his personal 10 favorite versions of The Joker. At first, it starts out parodic ("Train Joker"), but by the top 3, it's a pretty solid list. I dunno whether you've seen this by now (it came out 2 years ago) or what use it could have in writing references, but enjoy the hilarity.