Good resources for American history include the Library of Congress, the Smithsonian Source, the University of Houston's digital archives and Wikipedia. Between them these resources offer a blend of primary and secondary resources.
The Library of Congress allows users to explore American history according to each era. For example, The Americas to 1620 offers information on the first settlers to the establishment of the United States. Within each section there's a selection of articles, primary resources and nonwritten resources, including images. Examples include the Lincoln Papers and images of Christopher Columbus and his voyages. There's also guides on reading historical sources from different eras. The Smithsonian Source also offers primary and secondary resources, including digitalized images of medals, bank notes and official documents. The Advanced Search section allows users to search according to keywords, dates and other factors.
The University of Houston's digital archives features primary and secondary resources that users can explore according to topics, eras, voices and types of multimedia. The Voices section features narratives from different demographics, such as women, Native Americans, children and Asian-Americans. Teacher resources are available, including lesson plans and quizzes. Wikipedia is a selection of online articles that users contribute, and it offers a dedicated History of the United States section. This section offers information ranging from the prehistoric era through to the present day. Many of the articles feature references, including primary and secondary documentation.