I liked the currency system in Dragon Age. (origins)
Simple, and not too much unlike our own, here in the US.
100 bronze/copper pieces made a silver piece, 100 silver, a gold. Though, I forget at the moment what they're called-
I can google that.
Oh yeah, the gold pieces were called "sovereigns"...
http://dragonage.wikia.com/wiki/Currency
Bits, Silvers, and Sovereigns.
It adds a bit of interesting mix to the system when there's more than one unit.
I mean, in practically every other game it's one solid unit. Like Pokedollars in Pokemon
(though it's actually Yen- America just changed it- probably thinking "oh it's too Japanese, let's suck all the culture out of it!"), or Bells in Animal Crossing, or Rupees in Zelda, or bottle caps in Fallout, or rings in Sonic, or Koins in Mortal Kombat, etc, etc....
In games like that, they all have one unit of currency. Simple, yes, and I guess it's easier to program that way. But, Dragon Age is so far the only game I know that has more than one unit. It has three. ^^ And I find that more interesting than one flat unit.
I still wonder why in Animal Crossing they're called "bells".... why bells? Are they real bells? Like- cat bells? or school bells? or is that just the name of them? They look like coins, so they can't be real 'bell' bells. If they were, you'd jingle around while you were walking, and probably scare the fish and bugs....
.....then again, there is a ''jingling'' sound when you sell items... so, maaayyybeeee.........