I posted Thor & Captain America's working titles before, but it was not published because I didn't have a verifiable source.
Now, I have a new source. According to On Location Vacations:
"They’re at Raleigh Manhattan Beach Studio which is fitting since the working title of the film is now MANHATTAN."
Their source also tells them that their very anonymous tipster exclusively told them rehearsals are well underway this week.
Also--On Location Vaction didn't report this--but The First Avenger: Captain America's working title will be FROSTBITE.
"Read more:
Here"
"Under Creative Commons License: Attribution"