Having done my MA in the Book Studies department at Leiden, I can’t help but mention this new web service:
According to their web-site:
TitleZ makes it easy to see how a book or group of books has performed over time, relative to other books on the market. Simply enter a search phrase, book title, or author, and TitleZ returns a comprehensive listing of books from Amazon along with our historical sales rank data.
So, although intended for publishing professionals, this could be highly interesting for scholars of the (online) book trade. And currently, it’s free (whilst in beta). Perhaps they could be persuaded to offer academic licenses?