Chevrolet has opened up a site asking visitors to create advertisements for its ginormous SUV, the Tahoe, using a collection of clips and soundtracks, as well as your own text.
Thing is, there's no reason you have to make ads in favor of ginormous SUVs...
The good folks at Network-Centric Advocacy are collecting links to (and, where possible, recordings of) "Chevy Apprentice" ads talking about global warming and similar subjects. Here's an example. If you come up with a good one, be sure to post the link there -- and here, of course!