The emphasis here is individual-level data, with identifying characteristics of individuals taken away.
- IPUMS http://www.ipums.org/ Long time series of Census and CPS data. IPUMS is their interface to microdata, to provide custom extractions; NHGIS (above) is their interface to aggregated data and GIS layers.
- Data Ferrett http://dataferrett.census.gov/datasets.html Data from several surveys. Includes microdata, aggregated, time series, and longitudinal data. Allows customized tabulations.
- ceprDATA.org http://ceprdata.org/ Public microdata from several key surveys (e.g., ACS, CPS, SIPP) in Stata format.
