Resources for Rare Books: An Annotated Bibliography: Sixteenth-Century Books

• RBMS Latin Place Names Latin place names found in the imprints of books printed before 1801 and their vernacular equivalents.

Orbis Latinus Online The standard print equivalent: J.G.T. Graesse, F. Benedict, and H. Plechl. Orbis Latinus: Lexikon lateinischer geographischer Namen des Mittelalters und der Neuzeit, (1972).
 
Also of note is R. A. Peddie's Place Names in Imprints: An Index to the Latin and Other Forms Used on Title Pages (1986).

• English Short Title Catalogue (ESTC) Covers the period from the beginning of printing in the British Isles (ca. 1473) to 1700 for items published in Great Britain, it's colonies, or elsewhere in the English language. 

Early English Books Online (EEBO) Digital copies of books printed in England, Scotland, and Ireland, as well as works in English printed elsewhere. A nearly comprehensive representation of items cited in Pollard and Redgrave's Short-Title Catalogue (1475-1640), Wing's Short-Title Catalogue (1641-1700), and the Thomason Tracts Collection.

Early European Books Traces the history of printing in Europe from its origins through to the close of the 17th century, offering full-color, high-resolution facsimile images of rare and hard-to-access printed sources.

• Census of Italian 16th Century Editions (EDIT 16) An attempt to record all of the editions printed in Italy, as well as editions printed elsewhere in the Italian language, between 1501 and 1600. Counterfeits of Italian sixteenth-century editions printed in subsequent centuries are also included.
• Census of German 16th Century Editions (VD16) An attempt to record all of the editions printed in Germany, as well as editions printed elsewhere in the German language, between 1501 and 1600.

Bibliographies and Catalogues:

• Index Aureliensis: Catalogus Librorum Sedecimo Saeculo Impressorum. Aurelia Aquensis; depositum ac distribution Verlag Librarie Heitz, Baden-Baden, 1962- . An ongoing attempt to list all sixteenth-century books.  A sufficient beginning.
• Adams, H. M., compiler.  Catalogue of Books Printed on the Continent of Europe, 1501-1600 in Cambridge Libraries.  Cambridge: Cambridge University Press, 1967. The seminal publication on sixteenth-century printings, Adams’ Catalogue contains pages, collational formulas, format, author, brief titles, blank sheets, place of publications, printer’s statements, year, and copies available at Cambridge.  Also includes a printers index and information on particular towns and their printers.  The only shortcoming is that it is limited to works found in the Cambridge Libraries. 
• Shaaber, M. A.  Sixteenth-Century Imprints in the Libraries of the University of Pennsylvania.  Philadelphia: University of Pennsylvania Press, 1976. Similar to Adams, though less comprehensive in descriptions and limited to the University of Pennsylvania.