Iron Man & Tony's ingenuity
Thor & Asgardian ties
Hulk & Bruce's ingenuity
Black Widow & ties to SHIELD
Nick Fury (SHIELD)
Maria Hill (SHIELD)
(hahah.. she was hotter than SJ, to me).
Yeah... the movie roster.
Which foe would give them the biggest headache, or what areas are they lacking in?
DON'T tie this in to the villain for Avengers 2, at least not for another week or so; you can discuss that villain without saying that's the villain who's referenced in the movie.
The only thing that smacks me in the face directly is that they have no magic-wielders; Mjolnir has magical properties to it, but that's about it.