She-Hulk would be easy. Take five minutes on Edward Norton making a cameo, Jen getting hurt in the traditional "Ross almost catches the Hulk", Jen getting a blood transfusion, then she turns green and Fury shows up all "you're in the Avengers now KTHXBAI." Then you could use her as the viewpoint character to the Avengers (someone mentioned that X-Men was the only successful team movie out there, and it had Logan having all the "we're the X-Men, that's Magneto, stay away from my girl" exposition tossed his way, plus lampshading some of the ridiculousness inherent in the premise, which Shulkie was born for).
Plus you could have a nifty origin arc of her learning to control her powers. But really, so long as she looks at the camera at least once, I'll be happy. Or sees Stan Lee making a cameo and says "Do I know you from somewhere?"