Readers' Advisory Sites
You can only select 4 sliders at a time to choose which criteria to use for searching.
Try the MyMap feature. You can use it, even if you haven't registered, to explore other people's read-alike suggestions. Or, use the GoodReads option and link up with your GR account.
Site doesn't look like much, but when you enter a title or author it takes on a life of its own. (A gnod site, also offers same read-alike searching for movies and art.)
The closer the authors or titles are to one another on the page, the more people have cross-interests of the same author or titles.
Has a good subject category list to choose from, but you have to put in an author or title to begin a search first.

And, of course: GoodReads, Shelfari and LibraryThing.