You may find the following resources helpful:

Associations and Learned Societies:

Antiquarian Booksellers Association of Great Britain (ABA)

Antiquarian Booksellers Association of Canada (ABAC)

Provincial Booksellers Fairs Association (PBFA)

Royal Geographical Society

Royal Asiatic Society

James Caird Society

Books:

Americana Exchange

The Bibliographical Society

The British Library

Copac - Catalogue of University libraries across the UK

Worldcat  Search over 1 billion items in more than 10,000 libraries worldwide

The Ephemera Society UK

ILAB - LILA

Karlsruhe University, Germany - A virtual catalogue of books at different international libraries

Fine Books & Collections Magazine

Bodleian Library

Cambridge University Library

National Library of Scotland

National Library of Wales

Trinity College, Dublin

National Maritime Museum

Library of Congress

Other Websites of Interest:

Hakluyt Society

Repositories of Primary Sources
A huge collection of links to non-commercial holdings of manuscripts, archives, rare books, historical photographs, and other primary sources for the research scholar.