I loved Calendar Girl from the Batman animated series. She was only in one episode, but she had such a great look, such killer Gotham villain shtick, and put Bats through his paces...
A pity the character was only conceived as a one-off for the show, because she was great.
http://www.batman-superman.com/batman/cmp/cgirl.html
The only flaw with the episode is the chronology of it -- we're to believe she's attacking seasonally, kidnapping these people and holding them for months before finally planning to dispatch them? Crazy enough, sure, but the practical difficulties of that are daunting, since some of the victims would have been kept on ice for like seven months (?)
But otherwise, it's a great episode.
