Moon Knight was in the Avengers and he's crazy. DD should make the roster once. Or lead some kind of team on a consistent basis. I liked it when he led the Marvel Knights against the Punisher. It was a cool concept but just wasn't carried out fully.
Daredevil. Dude has got to be the most underrated character in all of Marvel. He's never even been on the Avengers though he's a Marvel legend.
Gravity. One of the best (if not completely original) characters that Marvel has come up with in a while. Runaways or Young Avengers would also make excellent series. (Of course, they would also make excellent comic series if their creators would actually, you know, create.)
They should do an animated Marvel Team Up and every week Spider-Man will team up with someone who'd never have their own shot anyway. Then phase Spidey out and give everyone a chance to shine. That would be sweet. Of course in the fist episode, Spidey and Wolverine have to save some kid or senator or whoever, and they do but Spider-Man has to split and the next episode is Wolverine with .... Daredevil. They do their thing and Wolvie is called away and then it's DD and.... CLoak & Dagger, and so on. Just like how they did the Marvel Team Up comic. I'd watch that in a second!
When he first appeared, his costume looked way too much like Invincible's, making it seem (at least to me) that Marvel was trying to rake in on that successful cash cow (inasmuch as a low seeling book from Image can be considered a cash cow).
What obscure Marvel character (to some people) would you most like seeing get resurrected for an animated only feature and please say why ?