(In no particular order)
I will also try to think of what some of their offense would be and thier and super move, as well as their affiliation within the game's plot.
I know a lot of DC fans would also like to play as one of the mainstays of the Justice League, and I think this one is the one entry on this list that will most likely garner a spot on the game's roster. I can imagine he will side with Batman and the rebellion, and his super move would be something along the lines of transforming into a massive, grotesque creature and beating the high holy hell of his opponent. Basic attacks would include things like laser beam eyes, and size and physical manipulation.
A lot of people have been talking about the lack of a male/female ratio in the game, and I think Ms. Kane is the perfect solution to balancing out the gender issue. Her fighting style can be different from Batman, integrating her tazer gloves, tear gas, and batons to pummel enemies short-range, with a bat grapple that would allow her to move similar to Cyborg's grapple arm. She would be siding with Batman as well, but would try her best not to get into contact with her friend Wonder Woman. Her super move would be something like Batman's first revealed super that was scraped. (The bat grapple/dropkick combo)
This character is obvious with the addition of Shazam to the roster, though this character would be an inbetweener to the conflict in the game. His power move would definitely be awesome and include saying "Shazam" and causing a massive explosion similar to the awe-inspiring one in the trailer for DC Universe Online.
I think this character would be a great comic relief, and obviously, siding with Bats. His super move could be anything, because his power is so limitless that the production team could have a lot of fun creating it as well as his basic attacks.
It's obvious DC likes this character because she's been added to the new JLA. She would side with Batman (I know, it's getting repetitive.) and her super move could include her stepdad, STRIPE (that's the big robot in the above picture). She can launch the enemy into space, and STRIPE could hit the opponent with a barrage of bullets, rockets, and flame blasts.
He's immensely powerful and would side with Superman, being the boy scout that he is, and his super move would no doubt be explosive. His offense would mostly be long-range, blasting his opponents with energy beams, then swooping in to deliver powerful melee attacks, such as spearing the opponent into the ground and uppercutting them into the air.
Leave a comment if you would add others to this list and let's hope Injustice:Gods Among Us is as good as it appears to be!