Harley Quinn aka Dr. Harleen Quinzel, is in the top 3 hottest Batman villains for me. Interesting point is that Harley Quinn first appeared in the Batman: The Animated Series (Bruce Timm) and was only supposed to be a small character for one episode. Due to her popularity her became a bigger part of the show and DC comics.
The character is a frequent accomplice/girlfriend of the Joker, and is also close to Poison Ivy, from whom she gained her immunity to poisons and toxins. The comic book version of Quinn, like the comic book version of the Joker, is more dangerously violent and less humorously quirky than the animated series version.
Here is some of my favourite pictures from over DeviantArt. Check them out and show them love.