Fiction Menu is a site that lets you search for books and movies by plot details. The methodology is very unscientific, so it's highly unlikely that you'll be able to find a book you half remember reading as a child. Really, it lets you search other people's descriptions of recommended books and vote their description up and down. The descriptions vary in quality. Here's the description for Crime and Punishment:
A poor student kills an old woman, money-lender. But money is not the only stimulus. The murder is grounded on the student's theory of morality.
Wow. Not much to go on.
Still, it's a great idea. If the site takes off it could become incredibly useful.