I like Harley Quinn as a character and think she's really interesting, but I admit that I know next to nothing else about Batman aside from Harley Quinn's story. (Or any comic book series, for that matter.)

I think kinda liked GlaDOS from Portal series, or Alma from F.E.A.R. series.

Yeah, Harley Quinn seems like a cool character. I don't know a whole lot about the Batman universe, and the most I know about Harley is that she's the Joker's girlfriend.
But that's really all you have to know when explaining her to someone who doesn't know who she is xP

I would say Misogi Kumagawa from Medaka Box, but while I haven't watched the anime, I did go and read the entire Medaka Box wiki....so I'll go with Date Masamune from Sengoku Basara. I've heard good things.

Funny because Harley Quinn is also mine alongside Poison Ivy. And to be honest Garnet from Steven Universe.

^I like Garnet a lot as well, despite having watched Steven Universe all of about once.