Most coinage in the Dark Country is either Western or uses the same system found in the West. Some are imperial coins that have been found in various caches and put back into circulation via adventurers; however, these are rare.
The Shield is the largest form of currency. It is issued by the various cities in order to trade between each other on a massive scale. It is incredibly rare, but it is not unheard of for it to be found in large numbers in old treasuries. They are called shields because they bear the arms of whatever kingdom or city minted them. They often have a picture of the current ruler on the obverse side. Shields are equal to platinum pieces in Labyrinth Lord.
A Gold Shield
The Guilder is the most common of the gold coins found in the Dark Country. While still issued in the name of a ruler or a city, guilders are backed by the holdings of a guild.* On one side they will have the face of a ruler, and on the other side they will have a symbol representing the guild that financed the coin. They are equal to gold pieces in Labyrinth Lord. Guilders found in Nightwick Abbey likely have the symbol of the Sword Brothers one one side and the face of one of the Hochmeisters on the other.
A Guilder Financed by a Mercenary Company
The Sold is the least common gold coin in the Dark Country. Most predate the founding of the most powerful guilds and were instead minted directly by cities or rulers. They typically bare the rulers face one one side and his or her coat of arms on the other. Some go back to the times of the Empire. Solds are universally smaller and usually more debased than guilders. They are equal to electrum pieces in Labyrinth Lord.
An Ancient Sold
Denars are the most common form of currency in the West and therefore also in the Dark Country. They are silver coins minted by rulers or cities and are marked in the same way as a shield, but are also much smaller. Denars are equal to silver pieces from Labyrinth Lord.
Two Silver Denars
Nummi are relatively rare coins made of bronze or copper. They originate in Zenopolis, but many of the Seven Cities issue them themselves. They are totally unknown in the West. Nummi are equal to copper pieces in Labyrinth Lord.
Two Bronze Nummi
Zenopolitans and Novgovites have their own forms of currency (both of which include both the denar and the nummus), but I'm too lazy to describe them right now.
*I am aware that historical guilders are named after the Dutch word for gold, but I don't really care and this sounded neat.