3. Iron Man 3: James Rhodes/Iron Patriot
Rhodey should have already crossed paths with SHIELD by now, but they inexplicably decided not to show up when Aldrich Killian look the President of the United States hostage in Iron Man 3. He could be called in to help a the team rescue a high ranking member of the U.S government, with Rhodes joining them in the field if his armoured suit stretches the AoS budget too much. Don Cheadle has already make said he'd like his character joining the Avengers: Age of Ultron cast and this would be a good way to bring him in to the fold. Give him a role in the main story, and then have him briefed on the Avengers Initiative in the episode's end tag.