Book trailers are a great way to encourage reluctant readers to want to find out more about a story, and to give confident readers a taste of different genres. Book trailers can be a way to show literature circle groups the novels they can choose from; they can be shown in the library during lunchtimes (if your library has an IWB or tv monitor); they can be a way to encourage students to contribute reviews to review sites, and; book trailers can also be a form of assessment.
Another website sharing book trailers - breaks them in to grade levels and could be a good starting point for students.
graet site for examples of Book Trailers