Postage stamps commemorating numismatics one way or another.

The ancient is a Roman Imperial (Greek city under Roman rule) commemorating a coin that commemorates Pythagoras. Interesting on another topic, it depicts Pythagoras (of Samos: Samion) pointing to a sphere on a column.  Pythagoras was the first Greek philosopher (we know of) who posited that the Earth is a sphere.

The US Stamps are pretty clear as is the Monaco, which celebrates a Double Gros (eight pence).

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Pardon the redirect, but at your leisure, you might want to follow
This site, I do not know personally, but I wrote about the presentation back in April '06.
http://www.zumbo.ch/stamps/

Attila Kovacs, I met online when writing about "Coins on Stamps" for the ANA "Internet Connections" column. 
http://kovasati.gportal.hu/