www.loc.gov/collections/- The Library of Congress digital collection is much more than just books! The digital collections include digitized writings, images, sound recordings, maps, sheet music, and web archives that encompass historical events from the U.S. and the world. Digital artifacts can be searched, browsed, or filtered based on subject, format, or collection.  

www.archives.gov - The National Archives and Record Administration is self-described as the "nation's record keeper," with information ranging from presidential records to census/genealogical information, from Federal court records to eyewitness accounts of historical moments. The research site for the National Archives, found at https://www.archives.gov/research provides a variety of search methods and includes tips for not only the National Archives, but also other online research sites. A listing of the current digital projects can be found here.

www.dp.la - The Digital Public Library of America amplifies the value of libraries and cultural organizations as Americans' most trusted sources of shared knowledge. Browsing the Digital Public Library of America's digital exhibitions allows the researcher access to curated views of the collection materials. One exhibition of interest is America During the 1918 Influenza Pandemic. 

www.si.edu - This collection of nineteen museums and research centers serves as "the nation's attic," holding materials of historical importance for the country, housing over 155 million items. The digital collections of the Smithsonian include 1.6 million digital images, recordings, and documents. Searching or browsing the digital collection can be done at http://collections.si.edu/search/. Over 16,000 manuscripts, photos, and sound recordings can be found in the Smithsonian Online Virtual Archives.

https://library.medicine.yale.edu/digital - Yale University's Harvey Cushing/John Hay Whitney Medical Library offers selected digital collections, including the Medical Heritage Library Collection and Historical Medical Poster Collection. 

https://digital.lib.uiowa.edu/ - The University of Iowa Libraries' Iowa Digital Library houses the digital replicas of many of the items found in Special Collections and Rare Book Rooms across campus.  By searching Collections, a researcher can get a quick overview of some of the most popular and thoroughly documented collections by topic.