first gut reaction was Firefly, but rethinking that, because it was made by Joss Whedon of several years ago, and while he's done some good work since then (Dr Horrible), he's also done some stuff that was pretty mediocre (Dollhouse). If The Avengers comes out awesome in the Joss-y way we've all come to know and love then sure, Firefly would be epic to have back (as long as Nathan Fillion could do Castle at the same time-or clone himself!), but I feel like Joss might have lost a bit of his touch.