Its tricky because Iron Man doesn't have a rogues gallery full of villains that could cary their own movie. Outside of the Mandarin and Obadiah Stane, you have guys like Justin Hammer and the Titanium Man and Crimson Dynamo. However, in the movie continuity, Stane will likely fill the role of the corporate villain with the Iron Monger filling the role of the armored villain. So Hammer, TM, and CD would seem like repeats. The others like Blizzard, Whiplash, Firebrand, etc. are henchmen-type characters.
I have my doubts at to whether or not MODOK would work in a live-action film, but a terrorist organization like AIM or Hydra could possibly work.