Frank Welker is practically everything. On one of the Futurama commentaries they said he has the longest listing on IMDB. Not sure of the accuracy of that, but it seem plausible enough.
Optimus Prime and Megatron sounded pretty badass, but honestly the rest of it seemed pretty lazy. The big decepticon satellite thing's voice in particular was just some guy doing a Dr. Claw impression.
Correction: It wasn't just some guy as you state. The reason why Soundwave sounded like Dr. Claw is because he was Dr. Claw aka Frank Welker who provided the voice of Dr. Claw in the Inspector Gadget cartoon. And that's also the voice he used for Soundwave in the G1 Transformers cartoon. They just tooled around with it in post production to get the signature Soundwave voice. Frank Welker was also the voice of the original G1 Megatron as well. So don't you even dare start bashing Frank Welker. I'm no fan of this movie franchise, but I do not fault the Voice Actors for making a living in their chosen career path.
And Tom Kenny used almost the same exact voice for the little guy as he did for Ratbert on the Dilbert cartoon.
He would indeed have one of the longest. Primarily because he get's brought in a lot to do animal noises and other vocal effects. He isn't always doing a cartoon voice. Considering Welker's IMDB resume has over 600
acting credits, 24 music department (vocal effects) credits, another 5 in misc crew, & 3 soundtrack listing credits (Futurama for the dogs "Walking on Sunshine", Troll for the chant, and Na na hey hey from Bender's big score).
The guy is just about everything. In Deep Blue Sea he did the parrot sounds, He does all the animal voices for The Simpsons,