Goodreads is a great site for readers, you can list what you've read and write reviews, etc. There are also some great groups there including one for Stephen King fans. They have a good forum with lots of interesting topics and a book club that reads a book each month and discusses it. They alternate between King books and books he recommends or that they would recommend to him.
I'm also a member of a book club there focused on Sci-Fi and Fantasy called Sword and Laser.