Discuss how different authors have approached the same genre. For example, compare/contrast how Jules Verne, H.G. Wells, Issac Asimov, Madeline L'Engle and Terry Brooks explored fantasy/futuristic universes.
Focus on one prolific author's growth and development over time. Research the external factors that may have influenced changes in style and subject matter.
Many a short story/novel has been adapted to film and TV. Read the source material, rent the video of the adaptation and discuss what was done well, what was done horribly and why certain scenes should/shouldn't have been included.
Perhaps your book club has culinary leanings and is only interested in cookbooks. Another group might be passionate about horses. Whatever drives your group, find as many different titles as have been written about the subject and enhance your collective knowledge.
The works of Jane Austen are perfect for mother/daughter book clubs, especially in showing that young women of an earlier era had just as much angst about romance as their modern counterparts.
Read the biographies of famous leaders throughout history and speculate how they would have addressed twenty-first century crises and social concerns.