It's going to be an interesting line-up. THR is saying the final Avengers will be: Scarlett Johansson as Black Widow (rumored, but now confirmed?), Chris Hemsworth as Thor, Chris Evans as Captain America, Don Cheadle as War Machine, Robert Downey Jr. as Iron Man, and now Renner as Hawkeye. No Ant-Man, and no Hulk, though he's still still rumored to be in the running. A deal hasn't been reached with Edward Norton, so if there is a Hulk, he may be recast or seen only in CGI form.
I'm very, very curious how they're going to explain Hawkeye. All of the Avengers (if that is indeed the final line-up) will have appeared in other Marvel films by 2012, but Hawkeye will be the lone wolf. Hawkeye was initially a villain -- wrongly accused -- until he met and fell in love with Black Widow, and decided to follow the path of good. I wouldn't be surprised to see The Avengers pay homage to that, and initially align him with the Big Bad of the piece. The mind reels, though. That's a very different line-up than anyone is used to, and it may prove a lot harder to pull off than the classic set-up. The cast is more than capable though. They will be good Avengers, if only the script and adventure is worthy of them.