Rep. Ron Paul talks about competing currencies on the House floor:
I rise to speak on the concept of competing currencies. Currency, or money, is what allows civilization to flourish. In the absence of money, barter is the name of the game; if the farmer needs shoes, he must trade his eggs and milk to the cobbler and hope that the cobbler needs eggs and milk. Money makes the transaction process far easier. Rather than having to search for someone with reciprocal wants, the farmer can exchange his milk and eggs for an agreed-upon medium of exchange with which he can then purchase shoes.
This medium of exchange should satisfy certain properties: it should be durable, that is to say, it does not wear out easily; it should be portable, that is, easily carried; it should be divisible into units usable for every-day transactions; it should be recognizable and uniform, so that one unit of money has the same properties as every other unit; it should be scarce, in the economic sense, so that the extant supply does not satisfy the wants of everyone demanding it; it should be stable, so that the value of its purchasing power does not fluctuate wildly; and it should be reproducible, so that enough units of money can be created to satisfy the needs of exchange.
Over millennia of human history, gold and silver have been the two metals that have most often satisfied these conditions, survived the market process, and gained the trust of billions of people. Gold and silver are difficult to counterfeit, a property which ensures they will always be accepted in commerce. It is precisely for this reason that gold and silver are anathema to governments. A supply of gold and silver that is limited in supply by nature cannot be inflated, and thus serves as a check on the growth of government. Without the ability to inflate the currency, governments find themselves constrained in their actions, unable to carry on wars of aggression or to appease their overtaxed citizens with bread and circuses.
Read the rest, and also see Dr. Paul's inflation tax page on his campaign website.