This from Den of Geek...
Louis Leterrier says new Avenger will feature in Iron Man 2 and Jackson, Downey and Norton set for Avengers in 2011
Louis Leterrier has revealed not only that Jon Favreau is currently writing Iron Man 2 with Robert Downey Jr., but that the sequel to the Spring blockbuster will feature a new character from the Avengers, after the brief appearance by Samuel L. Jackson as Nick Fury in the post-credits sequence of Iron Man.
Additionally Leterrier is reported to have said that 2011 will definitely bring Jackson, Downey Jr., Hulk actor Ed Norton and two other 'A-list actors' - presumably whichever A-listers get cast as Thor and Captain America in their respective upcoming movies that Marvel is also producing - together for the Avengers movie.
All of this news is brought to us via a DoG scooper who supposedly spoke with Leterrier right out of a meeting with Iron Man director Jon Favreau at the Marvel Night at the Grand Rex in Paris in early July.