From NPR, a list of 100 Must Reads for Kids 9-12. Not all books are appropriate for the youngest in this category. There is some discussion in the comments about whether To Kill A Mockingbird should have been included as it is frequently taught in high school English classes. I read it in seventh grade with the rest of my class. Of course, when I was in the 7th grade, it was a contemporary novel and issues pertaining to civil rights were in the news every day.
The Teen list from last year included a series I read in the second and third grade: The Betsy, Tacy books. It also included at least ten books or series that are in the Must Read List for 9-12 year olds, including To Kill A Mockingbird. Both list include many writers that write for both age groups. One book may lead to another by the same author. There is plenty to keep even your most voracious reader occupied.