There's a lot of data on the Web, but it's all very scattered. At the same time, there's a lot of data sitting on people's hard drives that we don't have access to. There are various reasons why people don't share, but mainly, they just don't see the point.
Infochimps tries to solve both of these problems with an open data marketplace.
If you're looking for data, search the Infochimps catalog, and you might find what you're looking for. The system is loosely structured and meant to be a publicly curated data place with a mix of open data and for-sale data. Some data sources are simply outgoing links while others are stored in Infochimps infrastructure.
If you're on the other side, and you have data to offer, you can put your dataset up for sale. Fill out some forms, specify your price, and let Infochimps handle the rest like storage and cataloging. Infochimps takes a 20% commission on each sale for their service.
Selling data is of course nothing new. Search for databases for sale, and you'll get plenty of results, but this makes it easier for individuals and small groups to make their data available. Oh, and you can make your data open also.
The main challenge I see here is making sure the cataloged data are of good quality. It's one thing when the data are open and free, but when you're paying money, you want to make sure you're buying a product that's worth the price.
Currently, there's a star rating system, but it's unclear who decides how many stars go on a dataset. There's also no way to get a data sample, so all you get is a description pre-purchase.
Clearly, there's still a lot of work to be done with the application, but there's plenty of potential.
Infochimps is currently beta testing. If you'd like try it out, there's invites for the first 100 FlowingData readers who sign up. Use the code 'dataflowing' when you register.
UPDATE: Infochimps has kindly provided 100 more invites in case you missed first. Use this code when you sign up: flowswithdata.