Index Google
Extensive catalog of book information, critical and reader reviews, and full-text search.  
Premier online audibook retailer with affordable subscription options.  
Online archive for C-SPAN’s award-winning author interview program. 800+ interviews.  
Free literature notes and study guides covering all academic subject areas.  
The British Library  
UK's leading research library. Catalog of 15 million books, newspapers, and journals. - Also see: Online Gallery (powered by Silverlight)  
Google Books  
Search the full text of books. Read books online.  
Free audio files for books from the public domain read by volunteers.  
Library of Congress  
Largest library in the world with a collection of more than 120 million items. - Also see: Digital CollectionsResearch and Reference Services  
New York Public Library  
One of the largest public libraries in the United States. Collection of 51 million items.  
Open Library  
One web page for every book ever published. Currently indexes 24 million books.  
Project Gutenberg  
30,000 free ebooks from the public domain to read on your PC, iPhone, Kindle, etc.  
Free library of educational textbooks that anyone can edit.  
Indexes collections from more than 10,000 libraries.  
social bookshelves  
Organize and share book lists. Receive recommendations.  
Share book lists and receive recommendations from other book lovers.  
Build and share your virtual bookshelf. Discover, rate, and discuss books.