Nielsen Bookscan and The Book Standard have just launched the Book Sales Research Service. Here's the gist: Access to "weekly and year-to-date sales figures for any edition of any book, from January 2004 to the present," broken down by regional sales and by retailers. And, instead of paying for a full-on subscription to Bookscan, you can get that info for just $85 an ISBN ($600 for ten, with additional discounts the more you want to see).

Of course, since it's a one-time deal, you actually shouldn't stop checking your Amazon sales rank, unless you really feel like paying $85 over and over to find out how well you did every week. But for nonfiction writers who want their proposals to demonstrate the market that will exist for their books, knowing how well the existing coverage of the subject has sold could be a worthwhile expense.