1) Harry Potter. Because the Avengers have needed a magic specialist for a long time. You can't always cross your fingers and hope that Doctor Strange is going to be at home to answer the phone instead of being on the tail-end of the 14th Dimension fighting it out with Freddy Krueger, can you? (Remember, Disney will own everything.) Harry brings real magical expertise to the table, he's survived at least two uses of the Killing Curse, and he's got that great teen/tween appeal.
2) Snake Plissken. Because if there's one thing Brian Michael Bendis has
3) Pikachu. You'd probably have to bring Ash along for the ride, here, sort of like how the Justice Society always had to hang out with Johnny Thunder even though you know they wanted to just stuff him in a dumpster somewhere and take the thunderbolt along by itself, but it'd be worth it. Anyone who ever played 'Super Smash Brothers' can tell you the little teleporting lightning mouse can be stone-cold brutal when the mood strikes him. Besides, how awesome would it be to have Doom cowering in fear on hearing "Pika Pika!"
4) Superman. Because if you're putting together a flagship comic of all the superheroes, how can you pass up the ultimate hero? He'd probably have to split time with his membership in the Justice League, like Captain America, but it'd still be a great addition to the title.
5) Hannibal Lecter. Hey, it still makes more sense than Wolverine.
Any suggestions you have for a great Avengers roster that involves non-Marvel characters? Toss it in the comments!