According to Hollywood insider(?) Perez Hilton, the third Transformers movie is a go, although Shia LaBeouf and Megan Fox, the stars of the first two flicks, have not been attached. Even director Michael Bay isn't part of the deal.
The projected release date for this starless, directorless feature is July 1, 2011, just in time for Independence Day. Transformers 2 is coming on June 24th, 2009.
It's my opinion that the only part of the film franchise that is totally and completely irreplaceable are the gigantic robots. You could have any halfway competent action director and any actors, and you'd still have a workable movie. What about you? Do you need to see Shia? Or do you like Transformers for the 'bots?