According to the New York Times website:

Like many organizations, we hope to encourage innovation through collaboration. When you build applications, create mashups and otherwise reveal the potential of our data, we learn more about what our readers want and gain insight into how news and information can be reimagined. We're hoping you'll show us what's next for The Times.

You'll need two things - an API key and this PHP class. With it you can search based on book type (genre), list date and get the information back in an XML format. The results are an easily parsable XML structure that includes the book title, publisher, ISBN number(s) and rankings for teh current and previous weeks.