A few months ago, it emerged that Iron Man 3 would film on ten stages at the Screen Gems studios in Wilmington, and preparations for the huge production are apparently in the early stages.  On Location Vacations points to a facebook update by Premier Casting which states,

"Received an email this morning. Iron Man 3 will use about 1,000 extras during the film and there will be over 550 crew jobs and will be shooting from May 2012 until January 2013 with a Memorial Day weekend release in 2013.”

As far as extras go, the production is apparently looking for background actors across all demographics, so if you want to register and potentially make your way onto the set in some capacity, check out Premier Casting.

After the two-year mad sprint through development and production between 2008 and 2010 on Iron Man 2, it looks like Iron Man 3 will have a bit more breathing room, with a sizable production period.  This marks the first installment in the franchise not to be directed by Jon Favreau, with Downey Jr.'s Kiss Kiss Bang Bang writer-director Shane Black stepping in for what is easily the biggest film of his career.  Black, most known as the screenwriter behind Lethal Weapon, is co-writing the third Iron Man with Drew Pearce. 

This will also be the first Marvel film to arrive after The Avengers, towards which the studio has been working for the last three years.  Iron Man 3 will be followed by Thor 2 in November of 2013.