Iron Man 2 (2010): BATMAN 2
Heroes: Bruce Wayne, Batman
Villain/s: Bane; Arkham Asylum inmates; Hugo Strange; Catwoman
Cameo roles: Dick Grayson (Robin?); Dinah Lance, Black Canary; Amanda Waller, CADMUS
Plot:
Now an established hero, Batman is met with a blow when the walls of Arkham Asylum are busted open by Bane. Apart from having to take down Bane, Batman is forced to deal with the released inmates — Scarecrow, Firefly, Victor Zasz, among others. What makes Bane frightening is not so much his super-drug-enhanced physical abilities, but his calculating intellect and his drive to ultimately break the Batman.
There could be some Dick Grayson in there, too, because Marvel Studios would not be afraid to use characters even though they may not necessarily put on their costumes right away. And Black Canary is an almost-perfect answer to the Black Widow cameo, though her motivations as a solo hero in Gotham might remain mysterious (is she a Bird of Prey? Who knows!).
Finally, the appearance of Amanda Waller, and the existence of CADMUS, could be teased — setting up the major running plot for future films.
(Post-Credit Scene: Black Canary meets Amanda Waller, despite showing no indication of having known her before. Waller asks her to make her report on Batman. Black Canary tells her she thinks Batman is trying to do good. Waller accepts this, then asks if she has ever heard of a place called Themyscira.)