-- War Machine is likely to be in the sequel, as Terrence Howard's Col. Rhodes had too little screen time in the first film. They want to make up for that, and give him a crack at wearing the suit.
-- The Mandarin is the overarching, behind-the-scenes villain, but he comes with a lot of racial and superpower baggage that is difficult to put on screen. Starships, dragon aliens, and ten magic rings that can upset the power of the universe don't really fit into the realistic universe Favreau has aimed to put Iron Man in. And yes, Favreau is concerned about how the various Avengers will fit into that world, too. Hulk and Captain America are feasible (and the cross-over has pretty much been forced on the former), but he's not sure about Thor. (Who is?)
-- The recent hostilities between Russia and the U.S. have made a lot of Iron Man's arch enemies current again -- and we might actually see Crimson Dynamo pop up. (I vote yes, so we can get the Black Widow introduced to audiences.)
-- Demon in a Bottle is coming. Expect to also see some elements of Matt Fraction's Iron Man run pop up -- the movie and his work have a real symbiotic relationship going on. There may even be a partnership forming ...
Now, isn't that a nice way to start the weekend? There's more where that came from on CHUD, but remember to come back and geek out in the comments.