At the recent Linuxbierwanderung - which happens to be the only vaguely conference-like thing I'm going to this year - Daniel Nagy delivered a very interesting talk on digital cash, followed by a demo. One of the other attendees issued his own digital currency. I exchanged some euros for some of his currency, and then bought beer using digital cash!
It's anonymous, fraud-resistant, supports arbitrarily small transactions, and is generally funky.
I'm not going to tell you where you can get the software or anything yet, because the user-friendly front-end is still being worked on, but I have a good feeling about this.
