1. A system for presenting entities mentioned in books, comprising: a non-transitory computer-readable storage medium storing executable computer program instructions comprising: an entity importance engine for assigning query-independent importance scores to entities of an entity type mentioned by books in a corpus, the entity importance engine comprising a references module for identifying third party references to sections of a book in which an entity is mentioned, assigning importance values to the sections of the book, and calculating an importance score for the entity responsive at least in part to the importance values, wherein the importance values for sections of the book referenced by third parties are elevated relative to the importance values for sections of the book not referenced by third parties; a search module for receiving a search query from a requestor and identifying a list of a plurality of books in the corpus that at least partially satisfy the query, and ranking the books in the list in an order based at least in part on the query-independent importance scores assigned to entities mentioned by the books; and a presentation module for presenting the plurality of books to the requestor in the ranked order; and a processor for executing the computer program instructions.