"The Münzkabinett of the Staatliche Museen zu Berlin is one of the largest Numismatic Collections in the world. The area covered by its holdings reaches from the beginning of coinage in the 7th century B.C. to 21st century Euros, its geographical scope from Finland to South Africa, from Berlin to Buenos Aires. In addition to more than 500,000 items (coins, medals, notes, tokens) the Cabinet also holds sealings, dies, and historical minting tools."
ArtStor - ~1 million high-resolution digital images of art, architecture, and culture with educational use permissions. NOTE you can limit your results to a particular time period. Contains many images of Greek and Roman coins