Good reads is a website that allows you to keep track of all the books you've read, categorize them, review them and then get recommendations based on the books you like.
It's like social networking but with book lovers. Goodreads is for books what IMDB is for movies. You can take part in discussions for your favorite books and see what others are saying about them. The site provides recommendations for other books you could read based on your ratings for books you've already read. It also allows you to search for books and compare prices around the web so you can find the best possible price when buying books.
It does mean that you'll have to take the time to rate/review things you've already read. You'll be looking through your book shelf to try to mark down everything you've already read which can be time consuming, but once you're done with that it can help you find things you've never heard of that you might be interested in.
There is also a mobile app so you can update your progress or check on your friends while on the go.