RSS Feeds for New Books in Amazon
See, for example, the "law" tag. Notice that there is a link to a RSS feed for that tag at the bottom right. There are lots of other, more specific, law-related tags, too. This could be a great acquisitions tool for librarians.
It's great for personal interests also. There is a tag search box at the top left on the RSS Feed page explanation. Try entering in a favorite subject, author or artist to see if a tag has been created.