Use the free web application, LibraryThing, to catalogue your books, see what people with similar tastes are reading, and share reviews.
There’s also an Early Reviewers program in which publishers provide free advance copies of books, for members to review. However, there are many more requests than copies available for most books, so your chances for a free book are slim.
Sign up is quick and easy — just enter a user name, password, and optional email address. With the free membership you can catalogue up to 200 of your books. For a $10 annual or $25 lifetime membership you can catalogue an unlimited number.
Update: 2020-03-29 — Library Thing is now free for everyone.
To add a book to your catalogue, just enter a few words from the title, or other info.
Click Search, and LibraryThing will return a list of matching items. Click on a book in the list, and it’s added to your library. You’ll see how many other members have added the book, and any reviews they’ve written.
There are over 480,000 members, and 30 million books catalogued, so you’re bound to find a few people whose collections are similar to yours.
Other features include special interest groups and a Local Connection page, that shows events, libraries and bookstores in your area.
If you’re an author, you can connect with your readers, and participate in an Author Chat. You can import a wish list from Amazon, or other sources, and export your library as a CSV or tab-delimited text file.