3. Taskmaster
This is a character that, if he appears, I think it should be in the upcoming Agents of S.H.I.E.L.D. Series, since Crossbones will appear in The Winter Soldier. Taskmaster might not be a very well known character, however his potential is a very big one. A villain that can learn their opponent's fighting skills by just looking at how they fight at the expense of losing his normal memory, he is definitely a great character to explore. If he is introduced it should be first as a villain in the S.H.I.E.L.D. series, since his story is related to the organization. But after that I believe that if he appears in another Marvel movie it should be either as a cameo, or as a supporting character. However if the character gets a good response, I think he should get his own spin-off series. I mean think about it, this guy chasing other villains or working as a mercenary would be one hell of a series. And since Daredevil and The Punisher's rights are back at Marvel, this could be a great way to introduce them again in the MCU.