Amazon.com - besides finding great deals on new and used books, fiction fans can read customer reviews and reprints of reviews from leading trade journals. Customer assembled 'favorites' lists and fan communities also serve as great sources for finding related fiction.
Online Book Clubs
Goodreads - See what your friends are reading. Keep track of what you've read and organize your book lists into shelves. Join a book club to discuss your favorite books.
LibraryThing - One of the world's largest book clubs, keep track of your entire personal library and connect with thousands of people who read what you do.
Science Fiction & Fantasy
Fantastic Fiction - bibliographies for over 20,000 authors and information on over 270,000 books.