Literature Circles Resource Center - College of Education - Seattle University
("information and resources for teachers and students in elementary and middle school")
Contains a number of suggestions for developing and maintaining Lit Circles.
Booklists for Literature Circles
Some of the links to book lists on the site have expired, so I've reworked the list, pasted it below without the expired URLs.
(Links taken from http://www.litcircles.org/Books/books.html)
Cynthia Leitich Smith's Children's & Young Adult Literature Resources
Boys Read: Turning boys into readers
Out of the Ordinary Teen Book Lists
The Lazy Readers' Book Club
Critical perspectives of indigenous peoples in children's and young adult books