Currency comes from many sources, and the smart trader is aware of the different sources and relative values. In the nation of Belfiad, several kinds of coins are minted. The king prints coins in three denominations. The Imperial penny is a copper piece, about the size of a modern-day US penny. The Imperial Silver Brillig is a silver coin the size of a quarter, and the Imperial Crown is a gold coin the size of a nickel. These coins are universally accepted throughout the empire at face value. Most of the dukes also mint their own coins, usually in the same denominations and sizes as the Imperial coins. These are usually accepted at face value in the duchy of their origin, but sometimes are looked less favorably upon in other duchies. There are no platinum pieces minted in Belfiad, though Candor does have a Candorian Double Crown, worth 2 regular crowns (minted in gold).
Most of the other nations make similar currencies. Several of the dwarven nations make platinum coins. Coins from other nations can often be difficult to get a common tradesman or laborer to accept. Merchant's will take them though often not at favorable exchange rates. Coins in treasures of monsters and such will often contain a farely random mixture of coins from several different sources.
The strangest of all currencies, is that of the Weslien elves. To the Weslien elves, gold and silver coins are essentially worthless, unless they have reason to journey into human lands. The Welsien elves use coins carved from rare woods or amber as money. Few other than the elves, see any value in these items. Orcs are known to collect some of these, using them as trophies of killing "pointie ears" (though the ears themselves tend to be more popular), but will rarely trade gold or silver for them.
Gems are commonly used as means of transporting and trading large amounts of money. Though since their value is difficult to tell accurately at first glance, and easily open to fraud the trader must be carefull. The King of Belfiad has been endorsing a program of government sponsered appraisers.
These appraisers supposedly have the King's Guarentee of fairness (though corruption still exists, especially far from the Royal Throne.) The appraisers will buy and sell gems, taking a 1-10% margin on each transaction. (Smaller gems have a larger margin than larger gems in general.)