You might be interested in the Hawala system[0] of money transfer. It has existed for hundreds of years, and allows efficient international money transfers with no central authority.
Hawala has fascinated me to no end, as essentially an anarchistic peer-to-peer web-of-trust banking system. It has existed for a long time, and keeps functioning even where traditional banking systems have broken down. As cool as Bitcoin is, I have more hope for a system akin to Hawala than some proof-of-work based system. Guerilla banking that depends on having more (computational) power than your enemies isn't too realistic. PGP'd remittances are much more cryptographically robust, and depend just on the one factor that any real monetary system relies on anyway: human trust.