interesting site: booklamp.org
This got my interest and given the readers we have on this site I think you'll peruse it as well:
http://www.booklamp.org/ .
"BookLamp.org is the result of an exploratory project intended to help you find new books by comparing the content of the books themselves, similar to the way that Pandora.com matches music lovers to new music. We're attempting to help you find books with similar themes and writing style to books you've enjoyed in the past - comparing elements like Description, Pacing, Density, Perspective, and Dialog - while at the same time allowing you to specify details like... more Medieval Weapons."
Biggest problem right now: not enough books in its database.