BadTaste has word from Chris Hemsworth that Natalie Portman will be returning as Jane Foster in The Avengers. It was also recently mentioned by Stellan Skarsgård himself that he would be reprising his role of Professor Erik Selvig in the film as well. They join an already impressive cast that includes Robert Downey Jr., Samuel L. Jackson, Chris Hemsworth, Chris Evans, Jeremy Renner, Scarlett Johansson, Mark Ruffalo, Clark Gregg and Cobie Smulders.
This news makes me wonder if Pepper Potts and Rhodey/War Machine will eventually show up in the film as well. As both Don Cheadle and Gwyneth Paltrow have given the impression neither had been approached and will stay in the Iron Man films.