I believe the "I am Iron Man" effect was achieved using a talkbox, where you run a guitar amp through a plastic tube inserted into your mouth, allowing you to create formants. Like the ones famously used by Joe Walsh and Peter Frampton. AFAIK they are still manufactured by Walsh's onetime business partner, Bob Heil.
You should be able to get close with a vocoder, but I think you'd have to add distortion like Guitar Rig or something similar.
[EDIT]I looked it up, and the Heil talkbox is still being made, but by Dunlop Manufacturing - the company that makes your guitar strings and picks.