Earlier today at Comic-Con, Paramount officially announced who will voice Optimus Prime in next summer's
Transformers Movie. It is the one & only Peter Cullen. That's right, the ORIGINAL English voice of Optimus Prime from the 1980s will be returning to his infamous character in the new movie. Cullen is also the long-time announcer for Toonami (the guy with the deep voice who's known for saying "Only Toonami"). The audience at Comic-Con was most pleased with this information.
Source:
http://www.aintitcool.com/display.cgi?id=23937