First up, Jon Favreau has confirmed that he will be reprising his role - not as director, alas, but as Stark's bodyguard/friend/gopher Happy Hogan. Favreau enjoyed an exanded role (and I'm not talking about his waistline) in Iron Man 2 and adding Hogan should go some way towards providing some light to set against the shade of the plot, if the rumours of Stark's descent into self-doubt, guilt and alcoholism are on the money.
Ben Kingsley has signed on, and with rumours the the Mandarin is likely to be involved, it doesn't take a genius to join those dots...
There has been some suggestion that the significant injection of Chinese finance into the film might mitigate against an Asian supervillain but the comparisons are just too easy to make to totally ignore.
James Badge Dale has allegedly been cast as Eric Savin. The Iron Man storyline in which Savin originally features sees him working for the government, before being blown up by a landmine, made into a cyborg by the woman he is sweet on and then transformed into a sort of sub-Robocop. There are suggestions that it won't play that way in the film, with strong hints that the plot will follow the Iron Man: Extremis storyline, seeing Savin pumped full of Extremis nanotech instead - giving him super strength, electricity powers and the ability to spit fire from his mouth. The casting of Guy Pearce has seen rumour suggest he will be playing Dr Aldrich Killian, the inventor of the nanotech who kills himself when he realises what he has created and the danger it will cause.
A match for a drunken Stark? You'd have to think so.
In the comics, Stark is forced to inject himself with the nanotech in order to level the playing field for a final battle with Savin, leading to a different relationship between the billionaire genius and his armour.
The Extremis storyline has already been mined for the franchise, with Stark's al Qaeda origin story finding its genesis there. It looks likely that they are going to follow through witht he rest of the tale.
The film sees the return of cast members Downey Jr., Gwyneth Paltrow and Don Cheadle, in addition to several newcomers including Guy Pearce and Rebecca Hall. It's scheduled to hit theaters on May 3, 2013.