Michael Bay has promised to fill the web with disinformation about Transformers 2, so take this with a grain of salt, but the newest Transformers movie should begin filming in June. The fan-site TFW2005 reports June 2 as the start date for the sequel to 2007's Transformers.
Almost nothing is known for certain about the sequel film, including the cast, although Shia LaBeouf is reported to be returning.
Filming will, most likely, begin in Philadelphia and Bethlehem, Pennsylvania.
Transformers 2 is scheduled for a June 26, 2009 release date.