I am the biggest fan of Marvel and their casting choices, but in the name of a contest-I couldn't resist my own alternate casting. Here's my first attempt; I'd love to hear your thoughts, as I'm sure I'll do another...
Iron Man: Colin Farrell
Colin Farrell is one of Ireland's best rising stars in Hollywood and abroad today. Known for many roles, including (some of my favorites) Minority Report (2002), Phone Booth (2002), Seven Psychopaths (2012), and Total Recall (2012), Farrell has the chops and rapport as an actor to pull of Tony Stark/Iron Man. His unfortunate involvement as Bullseye in Daredevil back in 2003 may have him off your list, but I truly think (while no one could replace Downey Jr.) he'd do a marvelous job. If Affleck can come back from that, anyone can.
Captain America: James Marsden
One of his most memorable roles to fans, particularly in this genre, is his role as Cyclops in the X-Men movie franchise. All too often type cast in the good-guy-who-doesn't-actually-get-the-girl roles, I believe that he can venture into the realm of Steve Rodgers, particularly if he beefs up a bit.
Thor: Luke Evans
Perhaps best known (in my mind) for his role in The Hobbit, Evans also has an impressive resume and charmingly foreign roots (being from Wales). Being that he's cast as Gaston in the upcoming Beauty and the Beast, I think he could thrive in the role of Thor as well (not comparing the two roles, just noting the muscles that would be assumed for both).
Hulk: Ethan Hawke
Hawke has been in films since 1985 and, while I remember him most clearly from Dead Poet's Society from years ago, has proven himself to be a very talented actor. I see him sincerely pulling off Bruce Banner, while executing the Jekel/Hyde side of the Hulk very well.
Hawkeye: Josh Duhamel
Jeremy Renner got the shaft when it came to his involvement as Hawkeye thus far and I'm very excited to see him play a larger part of the story in Age of Ultron, but if there was another person I could see filling his shoes it would be Duhamel. I don't know why, but when I think about the comics or even watching animated versions of Hawkeye, I see him really being able to bring not only the physicality of the character, but the wit and dry humor. I could be wrong, but it'd be worth a shot.
Black Widow: Margarita Levieva
The only thing that has bothered me about how Black Widow has been portrayed is that you really don't see the Russian part of her and, while I know that she's a spy and could pull off different voices and stuff, I want to see those roots. I haven't seen Levieva in too much, but from what I have seen I think she'd do a splendid job as Black Widow.
Fury: Laurence Fishburne
I don't think I have to do too much convincing to suggest Fishburne in this role. If we can't have Jackson, he'd be an easy second place for the role of Fury.
Share your thoughts and suggestions below!