One of the most popular series for teens is a limited-time free download in .pdf format! Of course, they're promoting Westerfeld's newest book, Leviathan, but who can complain about that? As more and more publishers make their works available in online forms, I can see more and more ways that you could leverage this free/cheap material for classroom use. Of course, the best aspect of the online text is its infinity - instead of having to police limited numbers of physical copies and tell students to hustle and read so others can have access too, every student could log in and read online, or download to their personal device-- no waiting.
On a related note, education stands to gain the most from asking publishers to give up on DRM and concentrate on better ways to maximize revenue.