How many times have you had a student ask you for a writer who writes like ________ or a book that is like _______? I came across this site on Larry Ferlazzo's blog called Literature-Map.
The short version is that you type in an author's name and it creates a cloud with that author and with other authors. The closer in the cloud, the more similar the authors are in writing style and/or content.
In addition to answering that hypothetical student's question, you could also use it as a support in purchasing decisions (as in, "I would like to find more books like what Stephenie Meyer writes.")
My one concern is that some author's names are spelled incorrectly. Still, a valuable tool.