Michael Bay made an official post at his website. Transformers 3 is his next picture. He had a five hour meeting in San Francisco and is now headed east to discuss the story and characters with Hasbro.  His small movie plan for Pain and Gail will go into production after Transformers 3 is in the can on July 1, 2011.

He left this note for Megan Fox:

P.S. Megan Fox, welcome back. I promise no alien robots will harm you in any way during the production of this motion picture. Please consult your Physician when working under my direction because some side effects can occur, such as mild dizziness, intense nausea, suicidal tendencies, depression, minor chest hair growth, random internal hemorrhaging and inability to sleep. As some directors may be hazardous to your health, please consult your Doctor to determine if this is right for you.

(Source)