Here is a one-line bash that will use the JSON channel from @swyx and return a sorted list of each currency that is connected to USD:
curl http://finance.yahoo.com/webservice/v1/symbols/allcurrencies/quote?format=json \ | grep USD/ | cut -d'/' -f2 | cut -c1-3 | sort
It works today, but can be changed in the formatting (and, of course, the structure) of the channel over time.
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