Can a trailer turn a 22-year-old book into one of the biggest selling books on Amazon.com?

OK, let's concede the technicality up front: The Watchmen trailer that was shown before The Dark Knight in movie theaters this weekend was promoting the forthcoming motion picture, not the graphic novel written by Alan Moore and illustrated by Dave Gibbons. Nevertheless, as Bully observed over the weekend, the book promptly vaulted into Amazon's top ten, and as of Sunday afternoon it was the #3 seller on the site, bested only by the new Stephenie Meyer novel and The Shack (that "surprise bestseller" about the Holy Trinity straightening out the messed-up guy). It's not hard to figure out why; in fact, the movie producers already knew—the Watchmen audience pretty much is the Dark Knight audience.

If you were going to create a promotional video for your book, where would you show it to ensure that it would be seen by your ideal reader? Now take the question further: Instead of distilling your book's message into a video, write a letter. Who would you send that letter to?