The foundation of all modern economies is energy, so it makes sense to me that ultimately money is just a measure of our ability to buy energy. Energy is the ultimate commodity, and the best basis for a global currency.
It has been suggested many times that the Kilowatt-hour will one day be the standard unit of exchange around the world, in the same way that wealth was once measured in gold, or buffaloes. One company is now trying to create this currency, in the form of the Kilowatt Card - http://www.kilowattcards.com/
The idea is that you buy the cards as a form of paper money. You can redeem the card at their website, and the company pays your electricity bill for you. They are trying to extablish themselves as a kind of clearing house for the trading of domestic electricity, and issuing paper against their future ability to pay for electricity.
The probability is that energy prices will rise as demand increases and fossil fuel reserves decline, so Kilowatt cards may be a good investment as the issuer will have to pay whatever price the utility company charges when you cash your cards in. It sounds like a great idea, but the organisation behind it is not being very transparent about ownership or assets - ie who is backing this new 'currency' and how do we know if they'll be able to redeem the cards in the future.
All the same, it's a great idea and if it was adopted by a reputable international organisation it could change global economics forever.http://www.kilowattcards.com/template/index.cfm