One of my favorite websites is Goodreads. If you love reading, this is the best site to organize, catalogue, and rate books you've read (or want to read). You can join book clubs, add friends, and best of all, Goodreads recommends books to you!
A little bit of detail on how it works: Of course, you have to create a profile with login information. From there, you can create bookshelves to begin cataloguing your books. In the beginning, I only had a few shelves because I didn't know what I was doing, but I recommend you create shelves for all the genres you read (or want to read). You can even create shelves with phrases like "started to read but had to return to library" or "wouldn't recommend to anyone to save my life." I even have a "might read" shelf which is stupid because I have about a thousand books on my "to be read" shelf. As if I'll ever get to my "might read" shelf.
To add books, you simply type in the book's name, author, or ISBN and it'll list the book with the cover, summary, rating, reviews, publishing info and a ton of other information. It'll list how others have catalogued it or if it's on any book lists (I'll explain momentarily). If you have a smart phone, you can actually scan the bar code to add the book to your shelves. This made adding the books I have at home super easy to add to Goodreads. My only regret was that when I scanned the hundreds of books I own, I didn't catalogue them. I wish I would've been a little more thorough in adding them to specific shelves because sometimes I'm looking for books to recommend to someone by a genre and all the hundreds I added in the beginning aren't catalogued. Cataloguing is easy. You simply click the check box next to the shelf and it's added.
Recommendations are one of the best features of Goodreads. Love the recommendations! Recommendations are based off of the books on each shelf and are per shelf. So if I have a biographies shelf, Goodreads will recommend books according to the books I have on that shelf. This is a great way to discover new books and authors in your favorite genres. You can also search "listopia" (which is thousands of book lists) to find new books and authors. As an example, if I wanted to search books published in the 1920's, I can find a list of the best books published in the 1920's by searching for the phrase "1920's."
Another great feature for recommendations are the book clubs. You can join as many as you'd like and there are thousands on the site. I joined a few in the beginning, but it was too much so I'm only active in one book club now, one that I joined a few years ago. It's a small group of women from all over the world and we choose books collectively by suggestions and voting. We have online discussions about our books and other topics, including games, new members, and birthdays.
There is so much more to Goodreads, but I'll end with the giveaways. There are hundreds of ongoing book giveaways. Winners are chosen randomly and you can enter as many contests as you like. I've won a couple books off Goodreads in the last few years and it's a nice surprise because I often forget I've won until a book arrives in the mail!
Goodreads is a very comprehensive site so in order to get an idea of all the features, you'll just have to sign up for yourself. For book lovers, there's nothing better.