The young adult novel is a literary grey area. Designed to appeal to readers from about age 12 to 18 (many facile readers are ready at ten), they often have protagonists in that age group. But perennial favorites of adults also are included, such as To Kill a Mockingbird. NPR has winnowed down suggestions to about 250 and now is soliciting votes from the public to pick the top 100. Go here to cast your votes.