Google Print has scanned and made searchable many books on ancient numismatics.
Google's user interface makes it easy to find phrases among thousands of books, but difficult to search by author or title. I've started keeping a list of public-domain titles related to (mostly) ancient numismatics.
Google lets users flip the pages but I've found no way to jump to a particular page or section.
Greek Coins and Their Parent Cities by John Ward
The Confessions of a Collector by William Carew Hazlitt
Description de Médailles Antiques, Grecques et Romaines (Volume 1) by Théodore Edme Mionnet
Description de Médailles Antiques, Grecques et Romaines (Volume 4) by Théodore Edme Mionnet
Description de Médailles Antiques, Grecques et Romaines (Supplement volume 3) by Théodore Edme Mionnet
Description de Médailles Antiques, Grecques et Romaines (Supplement volume 4) by Théodore Edme Mionnet
Description de Médailles Antiques, Grecques et Romaines (Supplement volume 9) by Théodore Edme Mionnet
Mélanges Numismatiques by Ernest Babelon
Coins and Medals: Their Place in History and Art by Stanley Lane-Poole
A Descriptive Catalogue of Rare and Unedited Roman Coins by John Yonge Akerman
Monnaies romaines et byzantines, d'or, d'argent et de bronze, monnaies grecques, gauloises, mérovingiennes, royales françaises, etc by Elzéar de Quelen
Description des médailles et antiquités composant le cabinet by François Jean Désiré Behr
Essai sur la numismatique mérovingienne comparée à la géographie de Grégoire de Tours by Gustave de Ponton d'Amécourt
Nouveau manuel de numismatique du moyen age et moderne (Volume 2) by Adrien Blanchet
Monnaies gauloises: Description raisonnée de la collection de M. P. Charles Robert by Pierre Charles Robert
Illustrated History of the United States Mint by George Greenlief Evans