The new (4th) edition of Who Next...? A Guide to Children's Authors was published last month by LISU, edited by two Librarians, Viv Warren and Mary Yardley. I just received a copy in the post as thanks for contributing to it.
It is a tool for parents and Librarians (and anyone else interested in children's books) to help them find authors that write in the same genre or on the same theme, so if they've found a book they love they could find similar things through this book. It is divided into the age ranges 5-7, 8-11, 12-14 and 14+, obviously not a perfect division because every child is different, but it is still a helpful way of determining whether the content might be appropriate. There is also a section that just separates by genre, and a list of useful websites and prizes worth perusing.
Worth a look methinks.