If you're thinking about launching Literature Circles, the Literature Circles Resource Center's Website is a TREMENDOUS resource. It provides a helpful overview and targeted suggestions for different grade levels.
One key thing to keep in mind is that there is NOT one right way to do Literature Circles. Figure out what your goals for the students are, set that purpose for them, and lay out the plan with clear procedures and expectations. The biggest problem I see walking around schools these days is that teachers fail to make the pitch before launching into the day's activities. Students want and need to know how what they are about to do is going to help them. It's worth the extra 90 seconds to provide a heartfelt rationale and remind students of The Big Picture.