Joss Whedon confirms there will be multiple Iron Man suits in the film. He explains how he used Marvel's requiest for multiple suits as a way to get back to the original design for Iron Man's chest:

"Marvel said, 'We like to see the suits evolve,' and I said, "Great! Then you're going back to the circle because the triangle is ass.' I'm a classicist. The circle has meaning, the triangle does not."

[Empire Online]