NNC includes approximately one million objects--more than 400,000 coins and some 550,000 pieces of paper money and encompasses the entire history of money of the world, coins and paper money, as well as medals.
http://americanhistory.si.edu/collections/subject_detail.cfm?key=32&colkey=9

Articles and reprints plus an outstanding electronic transcription of the British Museum numismatic catalogues, from Ed Snible.
http://snible.org/coins/

An online publication by Ed Snible of Barclay Head's 1911 corpus on ancient coins.
http://snible.org/coins/hn/

Coinage study and History of Bronze Imperial 249-253 AD.
http://sonic.net/~rbeale/mysite/

A Review of Numismatic Literature by Mike Locke
http://users.scronline.com/lockem/book_review.htm

Information about coins found in circulation for collectors.
http://www-cs-students.stanford.edu/~tjw/coins.html

An international association of miners, refiners, fabricators, and wholesalers of silver and silver products.
http://www.silverinstitute.org/

Greek and Roman Provincial coin reference. Historical and numismatic information.
http://www.snible.org/coins/hn/

Precious metals and rare coins investment source
http://www.stuppler.com

World plastic money catalog by Krause/Bauer
http://www.swschwedt.de/kunden/polymernotes/

The Sylloge Nummorum Graecorum is a British Academy Research Project, the purpose of which is to publish illustrated catalogues of Greek coins in public and private collections in the British Isles.
http://www.sylloge-nummorum-graecorum.org/