The US census bureau offers a wealth of data relating to the US population, including basic demographics, and much more.

The Integrated Public Use Microdata Series maintained by the University of Minnesota provides easy access to historical census microdata.

The Panel Survey of Income Dynamics (PSID) is a long-running panel survey that records many observations for the same people over time.

The Centers for Medicare & Medicaid Services (CMS) provide extensive data on Medicare, Medicaid, and health insurance.

The Nasdaq Data Link is a resource for financial, economic and alternative datasets.

Find more resources here.