Reading Groups for Everyone - Run by a charity called The Reading Agency and has lots of information about reading groups, news and special promotions.
BBC Radio 4 Book Club programme site.
Reading Group Guides - A US site with various guides you could find helpful in your discussions.
Whichbook - A different way of choosing a book by deciding on different aspects of a story, for example – happy, sad, short, long.
Booktrust - Aims to encourage people of all ages to enjoy books.