Personally I would like to see them combine some of the Masters of Evil characters with some of the Acts of Vengeance characters.
So essentially combine this: http://www.marvelarchive.com/images/cards/1_105-f.jpg
of course minus anyone that currently has rights with other studios.
with some of this: http://images2.wikia.nocookie.net/__...49/Detail4.jpg
and add maybe a few other characters like Crossbones to round out the roster and I think the Avengers would be in trouble.
That would be the Masters of Evil I would like to see.