Ok, so I'm going to break my rumour rule here for this post as their is no official quotes or confirmations anywhere, but this sounds really legit.
IESB are reporting that
Frank Welker is all but signed to reprise his role as the voice of Megatron in
Michael Bay's eagerly anticipated
Transformers movie. Apparently Bay and producer
Steven Spielberg have been overwhelmed with the fan support for Welker and
Cullen who were instrumental in the success of the original movie in the 1980's, and of course the latter already returning as the voice of Optimus Prime. We will keep you informed on this one and remember it's far from being set in stone, but this really does seem to make sense. Transformers fans happy with this? Sounds like a sensible choice to cast the familiar voices that helped make the source material so popular. source -
iesb