Have you heard of Literature-Map? Touted as "The Tourist Map for Literature," this site allows readers to type in a favorite author, then hit enter to find a map of similar authors. For example, when I typed in Katherine Paterson (author of Bridge to Terabithia) and hit enter, I got a map that included the names Chris Crutcher, Brian Jaques, Wendelin Van Draanen, Jerry Spinelli, and Louis Sachar. The closer the writer's names are to the center of the map (with the searched author's name), the closer the similarities between authors.
What does this mean? For students who know they like a particular author, they can type in the author's name and get the names of similar authors, then search the authors for titles they have written. The parameters of the search and findings are not given, so I am not sure how accurate these names are, but it can at the very least give students a "jumping off" point.
This is part of a larger site called Gnooks, which also has a search engine that allows students to type in the names of three favorite authors and get a name in return. When I typed in Margaret Peterson Haddix (the Among the Hidden series), Katherine Paterson (Bridge to Terabithia), and Louis Sachar (Holes), I got back the name Nancy Farmer, who wrote The Ear, The Eye, and The Arm, A Girl Named Disaster, and The House of the Scorpion, to name a few.