Early last year I started using Goodreads, which is an online book catalogue allowing me to keep track of what I've read and what I want to read. It also allows you to make up your own shelves to file them on, and recommend books to your friends. Pretty neat. So far I have rated about 570 books and have another 280 on my 'to read' shelf. Here is the cloud tag the site has generated to show where my interests lie- rather unsurprising results actually!
One of the best features of the site is that it then delves into what you have read and recommends new books for you to consider. Not everyone is a winner of course, but I have discovered a few authors I might not have otherwise encountered.