Teddy "Hulkling" Altman: "LEAVE MY FRIENDS ALONE!" Teddy is an interesting case in all of this. His files are a special SWORD case, so while he's registered, it's in a less 'maintstream' database. The problem is entirely going to come in that someone is going to do something to his teammates, I'm sure, and that temper is going to Hulk-gage. Totally cool with him being a camp escapee. Plus, I'd love if he could do some of his canon role, helping to unlock others.
Raven: Raven at first is cool with the Registration Act, honestly, but she's not a real citizen and doesn't have proper paperwork, so she's loping around it for now. Once she does realize what's going on, cause it's inevitable she'll get curious and come near the facilities, she's going to start helping those caught out as much as she can.
Professor X: Here's another good "Know what you did!" character! He will break down and register, in accordance with the law, especially after the date, and he's going to fight peaceably in public as much as possible until he's either arrested or has to go into hiding with others.
The Flash: Wally is SO uncertain! He wants to obey the law, so the pressure to register is significant, especially to keep Linda from having a bad rep. So unless she or his other cape friends talk him out of it, he'll register. The moment they try to get him to arrest said friends, though, or if they go after Bart or Linda, it's on like Donkey Kong.
Loki: "I do what I want!" He can also help push a bit of the catalyst, because if Wanda is caught, he's taking the bb and stomping any SHIELD agents who get in his way. Seriously. There might be death and major destruction if they try to stop him. He's also worming into the criminal underground, so if we're doing camp Gotham, he'll make an interesting slippery agent between muties and the criminals already there.
Doctor Doom: What? He's human with diplomatic immunity, bitches. ^_~