Paper Money Databases
Don Cleveland of Australia writes:

Martin Kaplan writes:

NGC Databases
David Lange of Numismatic Guaranty Corporation writes:

NGC Coin Explorer
NGC VarietyPlus
NGC Gallery

ANS Databases

MANTIS: The ANS Collection Database: MANTIS serves as the online home for the ANS's permanent collection. Hundreds of thousands of records, related images, and other contextual data areconstantly updated while new records are added regularly.

OCRE: Online Coins of the Roman Empire: Online Coins of the Roman Empire (OCRE), a joint project of the American Numismatic Society and the Institute for the Study of the Ancient World atNew York University, is a revolutionary new tool designed to help in the identification, cataloging, and research of the rich and varied coinage of the Roman Empire.

CHRR: Coin Hoards of the Roman Republic: Coin hoards of the Roman Republic Online is a database of Roman Republican coin hoards mainly from the period 155 BC to AD 2. This database beganlife as a personal research database constructed by Kris Lockyear using a combination of published data and Michael Crawford's personal archive now housed the in the British Museum.

CRRO: Coinage of the Roman Republic Online: Coinage of the Roman Republic Online aims to provide in effect an online version of Michael Crawford's 1974 publication Roman RepublicanCoinage (RRC), which is still the primary typology used for the identification of Roman Republican coin types.

PELLA: Coinage of the Macedonian Kings of the Argead Dynasty: PELLA is a research tool designed to present the catalog of the individual coin types of the Argead kings from Alexander I(ruled 498-454 BC), the first of the Macedonian kings to strike coins, down to Philip III Arrhidaeus (ruled 323-317 BC), the last of the titular kings to do so. Included as well as are the numerousposthumous civic and successor coinages struck in the names of the kings.

ENL: Dar al-Kutub, Collection of the Egyptian National Library: The Egyptian National Library's catalog of 6,500 numismatic pieces - coins, glass weights, dies, medals, etc. - is thethird major catalog of Islamic numismatic material held at the ENL, formerly the Khedivial Library, Egypt's most important library. This project is a result of the cooperation of the EgyptianNational Library and Archives and the American Numismatic Society with funding from USAID through the American Research Center in Egypt.

Art of Devastation: A Web-based Catalogue of First World War Medallic Art: The Art of Devastation is a research tool designed to help in the identification, cataloguing, andcontextualization of the abundant and varied types of non-monetary numismatic items issued during and immediately after the First World War (1914-1918). These items include art medals, commemorativemedals, and tokens, but do not include military decorations.

MANTIS: The ANS Collection Database
OCRE: Online Coins of the Roman Empire:
CHRR: Coin Hoards of the Roman Republic
CRRO: Coinage of the Roman Republic Online
PELLA: Coinage of the Macedonian Kings of the Argead Dynasty
ENL: Dar al-Kutub, Collection of the Egyptian National Library
Art of Devastation: A Web-based Catalogue of First World War Medallic Art:

To read the earlier E-Sylum articles, see:
A LIST OF COIN DATABASE WEB SITES (http://www.coinbooks.org/v20/esylum_v20n37a11.html)
A LIST OF COIN FORUM WEB SITES (http://www.coinbooks.org/v20/esylum_v20n31a14.html)
A LIST OF COIN BLOG WEB SITES (http://www.coinbooks.org/v20/esylum_v20n30a28.html)