3. Black Widow
Black Widow is a S.H.I.E.L.D. mainstay in the comics, acting as a super spy. Much like Winter Soldier, her allegiance has been taken into question on several occasions. The character has appeared in the second Iron Man movie as well as Avengers, and talks are on-going as to the status of a potential solo film for actress Scarlett Johansson. So if anybody on this list would be a bit of a stretch, it's going to be Black Widow. All the same, if we can get a twenty second Fury cameo at the end of an episode, why not give us Scarjo? She is after all one of the group's best field operatives. Maybe she can show up during a mission, where the team has to break her out of custody without knowing who they are actually going in to get.