Literary sites encourage reading and dialogue about books, which can be a catalyst for book sales.
Oprah's Book Club
http://www.oprah.com/index.html
Oprah Winfrey's highly influential online club.
African American Literature Book Club
Online book club devoted to promoting not just African American authors, but all kinds of books that may appeal to an African American audience - .
Book Crossing
Add books and track their journey from person to person, participate in book forums, and discover new books.
Crossings Book Club
http://www.crossings.com/welcome/
Monthly selections of books for Christian readers.
Barnes & Noble Book Clubs
http://www.barnesandnoble.com/blog/tag/book-clubs/
Retail giant now has a variety of book clubs to join.
Bookspan
Multiple clubs.
Goodreads
What are people reading?