It would appear that this is what Megatron will look like in the forthcoming (final?) Transformers movie, Dark Of The Moon. Revealed over at Joblo.com by an anonymous contributor.
Of course, this is just the toy version of the apparent new version of Megatron rather than a fully rendered CG model like we'll be seeing onscreen, but it gives fans a good idea of what to expect.
I kinda like it, and am pleased to see the arm cannon present. I can deal with him being a truck and not a gun, but the cannon is an essential part of Megatron's look. Personally I'm stoked for this new one, and am eager to see what this thing looks like in action!