This is another (more realistic) guess I'm making about the main villain / title character of "Transformers: Revenge of the Fallen." Due out June 2009.

As you can tell, this dude is pretty evil. He's so evil, in fact, that in the comics he is constantly on fire! The Fallen is sort of like the Transformers devil, he was one of the first transformers and he decided to worship destruction, and so he "fell" from grace or something.

In the movie storyline (I'm only theorizing here, but it might turn into spoilers if I'm right) it is because of The Fallen that Megatron (the main bad guy) decided to become evil in the first place, and so Megatron used The Fallen's face as the inspiration for the Decepticon symbol. See the resemblance?
Chances are that this fellow will show up buried under the Great Pyramid in Egypt, and cause some major problems for everybody. This will cause the Autobots and the Decepticons to team up, despite their differences. Whereas the first movie focused on the moral "no sacrifice, no victory," I think the moral of RotF, as hokey as it sounds, will be "work together."

my work here is based on the clues (vague highlights and silhouettes) that are present on the leaked RotF toy packaging, and on the thumbnails for the covers of the Transformers: Defiance comics (issues 1 and 2).