Considering The Avengers is doing such good business, and the MCU has, thus far, been pretty damn successful, Marvel have a golden opportunity to bring some of their more obscure characters to public appreciation; guys the comics fans will know, but the general public wouldn't.
They've already done this with Iron Man. Yeah, sure, people might vaguely have known the character from vague memories of comics or cartoons, but the movie and Downey Jr.'s performance propelled him to Spider-Man or Superman levels; the man on the street knows Iron Man. The same applies to a lesser extent to Thor and Captain America, and, choosing the right characters, could go further still. Launch franchises with lower-level heroes, and have Downey Jr, Evans or Hemsworth cameo and feature in the marketing.
Oh, and they need to lock Ruffalo down to a meaty, multi-movie contract. The guy's great, both as Banner and the Hulk.