In terms of ones that don't really haven't been brought up at all yet these would be mine
1st. Green Lantern Corps: Honestly how DC didn't make a Lantern an essential part of the Justice League is beyond me, I mean he's a founding member for crying out loud. Not only that but I have always thought that Green Lantern could be DC's answer to GOTG. The training on the home world of Oa, the defection of Sinestro and the forming of the Yellow Lantern's, the discovery of the other Corp's like Saint Walker's Blue Lantern's and Atrocitus's Red Lantern's. Just how stunning the battles and constructs could be if done right, DC really do have a potential big winner here and they would be smart to get it out before Marvel do Nova.
2nd. Red Hood/Nightwing: Now im not even a 100% what I would like to see here, a Red Hood movie, a Nightwing movie or a team-up movie with both of them. I just really like the idea of the movie being about both trying to move out of Batman's shadow, establish themselves as their own heroes and sort of try and figure out what kind of heroes they want to be. That's why I think a team up could work well with Jason taking a more violent approach than Bruce ever did and Grayson trying to reign in some of his aggression, you would have the inevitable conflict that would create.
3rd. Static Shock: Now I never grew up with Black Lightning so the show wasn't a necessary must watch for me. You know what I did grow up watching Static Shock! I loved this show as a kid and the character, the way he rode around on a man hole cover, with diversity in comics being an ever growing topic the introduction of a young black teenager would be a welcome addition to the team and he and Shazam could bounce off of each other really well with both being teenagers.