"the Data Hub is a community-run catalogue of useful sets of data on the Internet....This site is running a powerful piece of open-source data cataloguing software called CKAN, written and maintained by the Open Knowledge Foundation. Each 'dataset' record on CKAN contains a description of the data and other useful information, such as what formats it is available in, who owns it and whether it is freely available, and what subject areas the data is about. "

Read more at http://datahub.io/