Amazon Books. They claim to be the earth´s biggest bookstore. Try them!
Genealogical Publishing Co. in Baltimore, MD, is the largest commercial publisher of genealogical reference books, textbooks, and how-to books in the world.
Search the Advanced Book Exchange the World's Largest Source of Out of Print Material, they say. Let them prove that! (I found "The Danish West Indies ..." by W. Westergaard, price USD 150 - I´ve never seen it on the market before!)
IGR. Do you need to consult rare books? Perhaps this "look-up" service could help. Sponsored by International Genealogical Research, people are willing to look up genealogical information.
Digital Librarian of Book Collecting. A librarian's choice of the best of the Web listing sites and links. Maintained by Margaret Vail Anderson, a librarian of Cortland, N.Y.
Welcome to the Digital Librarian of Genealogy. A librarian's choice of the best of the Web listing sites and links maintained by Margaret Vail Anderson, a librarian in Cortland, N.Y.
Welcome to the Virtual Library of worldwide Museums listing addresses a.s.o.
Archives & Manuscripts from the Digital Librarian by Margaret Vail Anderson, librarian of Cortland, N.Y.
Reference site to the Library of Congress. Search the Libray of Congress Catalog, also links to other major catalogs as well.
Reference site to the British Library. The search system, OPAC 97, will allow you to find out what material is held in the major Reference and Document Supply collections of the British Library.