I'm less excited about a trilogy after seeing both the X-Men and Spider-Man nose dive in terms of quality: The sequels were, in my opinion, better than the first parts but the third parts were utter rubbish. Something to do with the number of villains being inversely proportional to the quality of the film. So long as they don't make the same mistake with Iron Man,it should be okay.
So The Mandarin for the second film and maybe Titanium Man and the Crimson Dynamo for the third.