Collider's Frosty was able to sit down with Michelle Monaghan during press for Source Code. He brought up her wonderful performance in Shane Black's Kiss Kiss Bang Bang opposite Robert Downey Jr. and asked if she'd be up for joining Iron Man 3. While Michelle says she talked with Shane about the film which focused more his own excitement. She left the door open saying if she was offered a role she'd take it but won't pursue.
Considering her friendship with both Shane and Robert it's likely her name could be thrown into the mix if there is enough interest from fans and Kevin Feige. Yet, Michelle might have had a bad experience with superhero films as she was in talks to play Silver Fox in X-Men Origins: Wolverine but ultimately didn't get the part. If I had to guess which role she'd be suited for would be either Whitney Frost (Madame Masque) or Jessica Drews (Spider-Woman). There had been speculation that Emily Blunt was up for a role in third film. As Emily has previously stated she never wanted to sign on for a multiple picture deal. Seeing Blunt playing a villain wouldn't be shocking. I'd personally love to see both of them in the third film and Gwyneth Paltrow take a backseat as the love interest.