In an article at Military.com talking about Terrence Howard's character Col. James 'Rhodey' Rhodes in Iron Man, the actor revealed that he will begin filming for Iron Man 2 in March of 2009.
The sequel has already been scheduled for a release on April 30, 2010. Jon Favreau is expected to direct again, with Robert Downey Jr. and Gwyneth Paltrow returning as well.
You won't have to wait that long to see Downey Jr.'s Tony Stark back on the big screen, however. Just catch The Incredible Hulk this Friday for a cool cameo.