Golden - Mapping all human knowledge
Goodreads - See what your friends are reading.
Sutle - Save and organize resources into a directed learning path.
LibraryThing - A home for your books.
Postly - Turn your photos into REAL beautiful postcards. Available on iPhone, iPad and Android. Make friends and family smile with a postcard!
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes