A number of people contributed places to find book trailers via OZTL_NET. Here they are in one place:
TrailerSpy – thanks to Ruth Buchanan.
Twilight # 2 – New Moon (Stephenie Meyer) thanks to Ruth Buchanan.
CMIS trailer Tuesdays thanks to Judi Jagger.
Jacketflap thanks to Barbara Braxton
On the topic of book trailers, local teen publisher Ford Street have a set of YouTube ads created by a fan who loves making trailers:
As with anything you show students, please remember to vet all book trailers first.