Buried at the bottom of an article about Shia LaBeouf switching agencies (for those into the agency thing he left WME and joined CAA) is a sentence that says:
LaBeouf recently wrapped Oliver Stone’s Wall Street 2: Money Never Sleeps, which opens in April. He’ll likely start work in May on Transformers 3.
This would be about right considering the release date for Transformers 3 is set for July 1st 2011.
When talking about the film last year director Michael Bay said that it can’t really get any bigger than Transformers: Revenge of the Fallen, so it’ll have to go “sideways” in terms of action and overall scope. He also said it will develop the relationship between Bumblebee and Sam further, explore more of the robot characters, and it could go darker.