Harley was a pretty shot term addition to the team, just the mission in Russia, but she does make something of a tie-in. I was thinking of Knockout for a bit (along with Giganta; I apparently have a thing for powerful redheads), or even Black Alice, but I think I'll go with Catman. I totally agree with the awesomeness of Deadshot as a character, but he just doesn't work for me in this setting.
Oh, and if anyone else comes in with any of the three characters I didn't choose, expect to find me pouncing on you rather quickly!