I was so frustrated trying to find appropriate lists for my young teenagers (and myself) that were challenging YET, age appropriate. I am compiling a list of links and plan to come back someday and compile a list of actual books! PLEASE feel free to suggest any other links you have found useful!
NPR Books: http://www.npr.org/books/
Arrowhead, WI library, college bound list: http://als.lib.wi.us/Collegebound.html
Teachers First (you can get lost here, I put you on grade 8): http://www.teachersfirst.com/readlist2-new.cfm?age=8
Reading.org Choices: http://www.reading.org/Resources/Booklists.aspx
Kumon Recommendations (pre-readers thru high school): http://www.kumon.com/miscellaneous/kumon_recommended_reading_list.pdf
Accelerated Reader: http://www.arbookfind.com/
(There are pros/cons to AR, I get that, but it is an excellent resource to just “check” an age level of a book you’ve already found. I had “little kids” ready to read at college level and not all material is appropriate!)
LibraryBooksLists.org: http://librarybooklists.org/index.html
Douglas County Colorado Library System: http://douglascountylibraries.org/
DCSDK12 RHMS Library Resources: https://sites.google.com/a/dcsdk12.org/rocky-heights-middle-school-library/
American Library Association: http://www.ala.org/alsc/compubs/booklists/summerreadinglist
GoodReads: https://www.goodreads.com/shelf/show/8th-grade-reading-list
Scholastic: http://www.scholastic.com/teachers/article/ready-go-book-lists-teachers
Classics List by The Guardian: http://www.theguardian.com/books/2003/oct/12/features.fiction
Classics by Eagle Forum: http://www.eagleforum.org/educate/1997/june97/list.html