Here’s Ethereum, which the Economist mentioned in the “Bitcoin’s future” article I posted earlier. Ethereum is a project that describes itself as “a platform and a programming language that … can be used to codify, decentralize, secure and trade just about anything: voting, domain names, financial exchanges, crowdfunding, company governance, contracts and agreements of most kind, intellectual property, and even smart property thanks to hardware integration.” It uses the concept of the blockchain as a decentralized ledger for all manner of transactions.
Here’s the whitepaper. It discusses related approaches (colored coins, metacoins) and details what they think Ethereum will look like. I haven’t read the whole paper.