Here are some links that might be useful for teachers using Lit Circles.
Some are arranged by grade, or theme, or both.
Themed Literature Unit Examples: Grades K-8
http://classes.seattleu.edu/masters_in_teaching/teed521/professor/Literacy/MITexample.html (Good suggestions but some of the titles are older)
ATN Reading List
Teen Book Lists and Reviews
Choosing Books For Lit Circles (Literature Circles Resource Center)
http://www.litcircles.org/ (Main Page)
Chapter One of: Literature Circles: Voice and Choice in Book Clubs and Reading Groups