Batgirl: Year One, Scott Beatty, Chuck Dixon, Marcos Martin (Illustrator), Alvaro Lopez (Illustrator)
This is the comic that made me fell in love with DC's Batman universe.
It's definitely not perfect but it's flaws can be overlooked with how kickass Barbara is and the great characterization. One of the better retcons. Although... Dick! Stop flirting with Barbs! >:(