An LA Times article today highlights two archives of great interest to students of US history: Photogrammar and Chronicling America.
Photogrammar is based at Yale University, and contains 170,000 photos commissioned by the US Farm Security Administration and the Office of War Information between 1935 and 1945. The photographs are actually housed at the Library of Congress but Photogrammar provides the access platform. It also includes an interactive map which lets users gather photos by region or date, and a Visualizations section which presents experiments in photo data. The photos, including 3,244 by Dorothea Lange, are mostly public domain, and all can be downloaded.
Chronicling America is a searchable database of US newspaper pages from 1836 to 1922. Jointly sponsored by the Library of Congress and the NEH, it contains over 10 million newspaper pages. Pages can be downloaded as JPGs or PDFs, and details can be excerpted.