Supergirl and Black Canary joins the Justice League as unlockable characters, no, heroes, in Justice League Heroes. You'll get to unlock the two PSP-exclusive super babes as you progress through the game, giving you another reason to give justice to the Justice League heroes by kicking ass on your handhelds.

Supergirl (aka the Last Lass of Krypton, hehe.) will have the following powers that you can use:

Flying Strike: Supergirl damages and crushes her enemies as she flies and zips through them.
Heat Vision: She can incinerate everything that falls in her line of vision via a searing beam of heat that erupts out of her eyes. You might wanna think twice before trying to catch this girl's eye.
Super Breath: No, not with super bad breath, but with a giant freezing breath, Supergirl can literally make guys stop in their tracks, all frozen and rigid. Of course she can do this to her girl enemies too.
Super Punch: A damaging blow that gets even stronger as Supergirl winds up.

Black Canary also has quite strong powers you can use if you decide to take on her role in the game. These are the powers you can access when you play as this tough chick:

Sonic Scream: Black Canary can scream a cone of disrupting sonic energy, resulting to stunned and damaged foes.

Bird of Prey: A powerful series of martial arts moves.

Talon Strike: A deadly combination of kicks that causes major damage to enemies.

The Raptor: A flying, spinning kick that tornadoes through a pack of enemies, damaging those in her path.

Yes, it's time that the girls get the spotlight on this game, and to give you a taste before you get the game on November 10, here are two screenshots of the two super babes in action (and no guys, not THAT kind of action):