Compendium of Federal Datasets (mother lode of datasets)
EPA Data (lots of it!)
National Bureau of Economic Research (NBER)
Center for Human Resource Research
Pregnancy Risk Assessment Monitoring System (PRAMS)
Healthcare Data (Susan White @OSU)
Ohio Medicaid Assessment Survey
Integrated Perinatal Health Information System (IPHIS)
DDE & PCBs in the Collaborative Perinatal Project (CPP)
Norwegian Mother and Child Cohort Study (MoBa)
Pathways to Adulthood: A Three-Generation Urban Study, 1960-1994
Inter-university Consortium for Political and Social Research
Ohio State University Research Data Repository (RDR)
National Health Interview Survey (1963-present)
Mid-Ohio Regional Planning Commission
EPA Smart Location Database (built environment)
Demographic and Health Surveys Program (global health data)
Social Explorer (thanks to Tyler Gorham for the tip)