Book Cover Images (BookChaser.com)
Here is a fun resource called Book Chaser for looking up book covers.
It is an experimental tool that lets people compare what book covers are available through different APIs. It uses four underlying services to look up that information: LibraryThing’s covers API, OpenLibrary’s JSON API, Amazon’s Associates Web Service, Google’s Books API and Worldcat’s xISBN.
You need to know the ISBN for the book, but it accepts both ISBN 10 and 13. It would be much easier to look up items by the title of the book or author, but it is still a fun resource.