According to these sites, http://jalopnik.com/399551/new-set-pics-from-transformers-2-show-audi-r8-buddying-up-with-corvette-concept
http://www.zercustoms.com/news/Audi-R8-in-Transformers-2-Video.html
the upcoming Transformers: Revenge of the Fallen will feature a 2008 Audi R8 (Typ 42) . So we can start with this listing
(IMDB link http://www.imdb.com/title/tt1055369/ )

It's also supposed to feature a 2010 Chevrolet Volt, but a replica. Mostlikely a Malibu or Cobalt underneath.
http://jalopnik.com/5043340/chevy-volt-fully-revealed-with-corvette-centennial-concept-in-transformers-2-set-video
http://www.edmunds.com/insideline/do/News/articleId=131426

And the Corvette is the Chevrolet Corvette centennial Concept
http://jalopnik.com/5034285/exclusive-the-transformers-mystery-car-is-the-corvette-centennial-design-concept
http://jalopnik.com/398674/mystery-corvette-concept-from-transformers-2-movie-gets-new-beauty-shots-multiplies

Here you are the image for the Audi R8 from the trailer: