Transformers movie characters

I'm having a hard time matching up the cars with the Transformers robots. The car design is completely fragmented in the making of the robot. I can't easily tell which robot came from which car.

I've circled the cues I've found, but there aren't a lot of them.

And is it noteworthy that all the cars are General Motors products? Hmm. Wonder why the movie makers decided to do that?

(Pictures are from the Yahoo movie site.)