Well, turned out to be interesting post and replies. Oh and I hope you are jesting when saying you like rigma. Megma, schmegma.
Seems like bartering should be part of game. Maybe slavery. Or both, "My 2 Magnar warriors for your 3 Tarth maids?" or "Your Fire Shard for a Resoln mage?"
Some have mentioned making currency with the likeness of your Soverign. Nice touch.
I think you should have some original names for the currency. Gold, Silver, Copper while simple and easy to understand doesn't make for much immersion. I also agree with those who believe that the economy can be based on any commodity or representation. Time was mentioned earlier as a means of keeping track of income. That idea would have to be expanded on greatly, but has definite possibilities.
I also enjoyed Connaer's naming idea- "The destruction of all the old civilizations brought on by the war of the Titans took away the reason for money. So the survivors reverted to the bartering of old, and went back to weighing things to assure fair trade. As time went on some semblance of order appeared and new terms of the weight and weighing became the the root of new currencies. So as the ancient Greeks of our world created 'Stater' as a coin ( literally meaning 'weigh') I'd suggest that Skael be the new coin, as it refers to the scales used to weigh items of worth. This word is similar to the Old Norse word skål which meant a cup or shell used as a measurement"
Some other possible names for the currency-
Chit, Silver Urx, Heads
Rod, Light Soule, Resoln
Yit, Yith, Yithrii
Dagk, Menoir, Nar
Axes, Dripping Axes, Krax
Just some possible Empire currency names for now..