Used Book Central  
   Searches the stock of affiliated dealers in the US.
   http://www.usedbookcentral.com/

Bibliophile  
   Multilingual book search engine.
   http://www.bibliophile.net/

Book Avenue  
   Search affiliated booksellers for out-of-print, used, rare and antiquarian books.
   http://www.bookavenue.com/

TomFolio.com  
   Searchable database of used, rare and collectible books from a group of booksellers.
   http://www.tomfolio.com/

Bibliopoly  
   Multilingual, international search for antiquarian and rare books.
   http://www.bibliopoly.com/

abebooks.com  
   Search the inventory of thousands of independent booksellers located around the world. Specialities include: used, rare, and out-of-print books.
   http://www.abebooks.com/

BookSearcher.org  
   Large online database of used, rare, hard to find, out of print, antiquarian and collectible books.
   http://www.booksearcher.org/

ABooksearch.com  
   Searches databases of participating booksellers.
   http://www.abooksearch.com/

Worldbookdealers  
   Searchable database of titles from international antiquarian booksellers.
   http://www.worldbookdealers.com/welcome/

Biblion.com  
   Antiquarian and rare books from primarily UK book dealers available on a searchable database.
   http://www.biblion.com/

ZVAB  
   Search for old, rare and out-of-print books. Access to many bookstores. Bilingual, English and German.
   http://www.zvab.com/

Big Words  
   Compares textbook prices at four stores - buying or selling.
   http://www.bigwords.com

Cover to Cover Antiquarian Books  
   Offering a range of antiquarian, second hand and out of print books.
   http://www.covers.freeuk.com/

Antiquarian Books in Scandinavia  
   Search the databases of the Scandinavian members of ILAB, International League of Antiquarian Booksellers.
   http://www.antikvariat.net/

Used Books Search  
   Search for used, rare and out of print books.
   http://www.usedbooksearch.co.uk

Ardis Online Database  
   Searchable database of secondhand books from UK booksellers.
   http://www.ardis.co.uk/index.html

Biblio.com, Inc.  
   Searches databases of associated independent booksellers worldwide.
   http://www.biblio.com/

Wantedbooks.com  
   Comparison search capabilities for finding rare, used and out-of-print books from many independent sellers.
   http://www.wantedbooks.com/

Library Book Sales  
   Matching book buyers with quality books that have been donated to libraries or are duplicate copies, monographs or surplus materials. Ex-libris titles are discouraged but not excluded. Library types participating: public, private, institutional, specia
   http://www.librarybooksales.org/