Change.org is a kind of public idea tourament. There are a bunch of different subsections: agricultural policy, government reform, energy, etc. Readers vote and comment on the ideas, and the top few ideas in each category advance to the next round. Larry Lessig has submitted Citizen Funding of Congressional Elections whereby only public money and small contributions can be applied toward election campaigns.
Not sure how well this kind of system can work. Many of the highest rated ideas don’t sound very productive…