The CensusCity SDK provides data to work in projects related to population, income, and any other Census data. It has been designed with modularity in mind to interact with Census Bureau APIs, Energy Information Agency, USDA Farmer's Market directory, and Socrata. Community modules include ArcGIS and U.S. Housing and Urban Development. Get started at http://uscensusbureau.github.io/citysdk/gettingstarted.html
Our API directory now includes 39 statistics APIs. The newest is the NISS API. The most popular, in terms of mashups, is the Compete API. We list 13 Compete mashups. Below you'll find some more stats from the directory, including the entire list of statistics APIs.