As if there weren't enough rumors floating around about casting for Thor, here comes another one. Nikki Finke at Deadline Hollywood Daily recently wrote a bit about possible casting for the film, and mentioned that she had heard that Natalie Portman was up for the female lead in the film.
Now, this mention comes at the end of a long list of possible male actors who are up for Thor, including Alexander Skarsgard, who has already been reported by several sources as a strong possibility. Additionally she says that the following actors have been tested for the role; Charlie Hunnam, Tom Hiddleston, Liam Hemsworth and Joel Kinnaman. She also mentioned that she had heard that Josh Hartnett had been tested for the role, but she listed him as a contender for Thor himself, instead of as Loki.
There was no mention as to which character Portman is being considered for, other than as the "female lead". From reading the comics, the obvious choices are either as Sif, Thor's beloved from Asgard and a warrior goddess in her own right, or Jane Foster, who is a nurse that falls in love with Thor's mortal alter-ego, Donald Blake.