post via +Jez Gordon. It's companion article is The Top Ten Types of Magical Currency.
10) Runic Arcanite: It works a lot like Bitcoin, only using actual labor and value. It can be used to power magic items and enchantments, but must be mined and constructed from raw materials (+Dallas M)
9) Ceramic Coins: Originally from Dark Sun, these are glazed, hampering counterfeiting (+Geek Ken)
8) Boon Debt: Mimicking the relationships of the eternally damned, every good transferred, also transfers a specific amount of labor debt. The value of your time is equal to what you can provide. In many underworld economies, this has indebted thousands of goblins, orcs, and ogres to overlords who will dominate their time for years to come. After your debt exceeds twice your lifespan, your very life is at their disposal. (+Geek Ken)
7) Light: Anything that produces illumination is of value in underground environments. Magical light is not at the top of the list; instead ranking near bioluminescence and other sources of uncontrollable light. The candle is the basis for such a system, with lanterns and lantern oil near the top. Torches are less useful than candles for the degree to which they foul the air. (+Jeff Russell) (+Jacob Hurst)
6) Animal Parts: Usually of rare or dangerous creatures. This follows one of the key functions of economic materials, which is that the more people that seek to acquire the substance the more rare and difficult to acquire the substance becomes. Feathers, scales, teeth, preferably of dangerous beasts all work quite well as currency.(+Jacob Hurst) (+Jeff Russell)
5) Occultum: Psychic particles bonded with gold that makes shadowy weightless high value coins that cost nothing to carry, but that lose value every time they are counted or observed as they shift back to gold (+Patrick Stuart)
Just as an aside. Damn dude. Patrick Stuart is astounding. He should just record himself speaking, constantly, as a service to mankind.
4) Letters of Credit: For when you want to just say 'to heck with it' and have everyone use paper money. (+Barry Blatt)
3) Mushrooms: Or fungus or mold, or other rare delicate plants that can be traded, smoked, and or consumed when dried. Tobacco, Coffee plants, and other natural drugs are also sporting commodities.
2) Water: on a crapsack world, in a grimdark era, basic water is the exchange unit in the world. Difficult to transport, in constant need and use. Other examples from this type of currency include steel, weapons, armor, food, threats of violence, and other basic expectations in a civilized society.
1) Gems: Nothing is more portable, rare, beautiful, difficult to acquire and valuable than shiny rocks. Strange but true.