Antiquarian Books Reference
The Antiquarian Booksellers Association of America has a fine web site - features include"find a Book" and "Find a Bookseller", as well as information about book fairs and a Collectors' Corner.
The Beinecke Rare Book and Manuscript Library is Yale University's principal repository for literary papers and for early manuscripts and rare books in the fields of literature, theology, history, and the natural sciences. In addition to its general collection of rare books and manuscripts, the library houses the Yale Collection of American Literature, the Yale Collection of German Literature, the Yale Collection of Western Americana, and the Osborn Collection. The majority of the Beinecke Library's holdings are cataloged online.