If you're interested in Bitcoin, you may want to check out several other attempts at creating decentralized digital monetary systems.

The Ripple project is creating a system where each node can issue their own unique money, and where transactions occur over paths of mutual trust: http://ripple-project.org/

I just released Rivulet, an alternative Ripple server that should be useful for website owners who want to let their users engage in user-to-user transactions without having to centrally distribute currency to them: https://github.com/jplewicke/rivulet

Pelle Braendgaard has proposed OpenTransact, a standard for RESTful digital transactions, so that we can escape from this mess of incompatible APIs and help people transact in their choice of currency: http://www.opentransact.org/