Pricepeek - Compare prices of the same product across all Amazon locales
Goodreads - See what your friends are reading.
Luzme - Never pay full-price for an ebook again
LibraryThing - A home for your books.
Savings.com - Compare prices at local stores & discover the best deals
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes