Users join a group of 6 and rotate books each month...so you contribute your own book and read 5 others that are sent to you each month. It's pretty cool...and it's free. So far I've read some great books.
Go to any small, independent bookstore and you are likely to find the most current issue of the Booksense newsletter. Each month, a list of book recommendations is compiled, based on recommendations from independent bookstore employees. There are also specialty pick editions that focus on a specific theme or genre. These books might not all be on the best seller lists, but they are wonderful books nontheless.
I hype this site pretty often - it's an e-mail book club (actually, a dozen of them, and you can sign up for as many as you want) that makes weekly selections and e-mails you daily excerpts. It's a convenient way to sample books, and I've found a lot I wanted to read further after getting that taste.