5. Black Nick Fury
The director of SHIELD was never among Marvel's most prominent characters, and if anybody can change that (other than Marvel themselves), it's Samuel L. Jackson. He's no stranger to video games, having voiced Afro Samurai and Tenpenny from GTA San Andreas, but the ability to actually control his digitized likeness would certainly be welcome. Besides, Capcom's side in MvC3 has the Resident Evil trio, so another gunslinger would be a great addition to Marvel's side.
4. The Punisher
Frank Castle is one of the most underrated characters Marvel ever created. He's the closest they have to Batman (and everyone loves Batman), especilly the Dark Knight Batman. He's dark, anti-heroic and doesn't let the lack of supernatural abilities slow him down. He doesn't need any gimmicky gadgets either - opting for good old lead instead, making him that much more unique. Just like with Samuel L. Fury, another gunslinger would only help the Marvel side. His theme would be a great addition to any soundtrack
The Daywalker is no doubt one of Marvel's coolest and most overlooked characters. He would fit in very nicely in MvC - his sword gives a lot of options for meele moves, his pistols and thrown weapons provide tons of room for ranged attacks and his vampire powers and/or the frenzy would result in some awesome specials. He definately deserves more than a cameo appearance.
Johnny Storm is an obvious choice for Marvel vs Capcom. He was set to be in Marvel vs Capcom 3, but was reduced to a cameo at the last moment. According to the developers it's because not even the current gen consoles have enough RAM to handle all the special effects he'd bring to the table. That's right - The Human Torch is just too good for MvC
You know how pirates and ninjas have been locked in an eternal struggle over who's the coolest? Well, Kurt Wagner brings the best of both to the table. His ninja-like mobility and teleportation along with his graceful pirate-like swordplay have tons of potential for great moves in MvC. His animations are sure to be fluid and flashy, making him very fun to play or even just look at.