I think Bitcoin is the Linux of payments. Everyone always talked about the potential to completely change the desktop (consumer use) but the real impact was the network/backend (Sun/NT machines) So Bitcoin is exciting to me but not as a payment method. But as a backbone it gets really interesting.
Less bitcoin itself, but the blockchain technology that backs the currency has a number of novel uses. The idea of a public, cryptographically secure and verifiable ledger could be used in everything from voting to domain name registration.