The 1994 one-shot graphic novel by Paul Dini and Bruce Timm will finally be released as a hard cover collection this May!http://dccomics.com/dcu/graphic_novels/?gn=11319
"Mad Love" is the dark origin of The Joker's sidekick Harley Quinn, the character introduced in the 90's Batman: The Animated Series. The story was actually adapted into an episode of the animated series in 1999.
http://en.wikipedia.org/wiki/Mad_Love_(comic)