Digital Library - The New York Public Library
http://digitalgallery.nypl.org/nypldigital/index.cfm
Special collections of photographs:
Performing Arts in America 1875-1923, A Hudson River Portfolio, Surveyors of the American West, Images of African Americans from the 19th Century, African American Women Writers of the 19th Century, Afro-Cuban Culture, Rodgers and Hammerstein Archives, Dance Heritage Coalition, Humanities Berg Collection of English and American Literature.

Documenting the American South
http://docsouth.unc.edu/
Southern history, literature and culture from the colonial period through the first decades of the 20th century. Collections include First-Person Narratives of the American South, Southern Literature, Slave Narratives, Southern Homefront, 1861-1865, Church in the Southern Black Community.

Gifts of Speech: Women's Speeches from Around the World
http://gos.sbc.edu/
Browsable and searchable. Special collection of Nobel Lectures and Top 100 American Speeches.

Internet History Sourcebooks Project
http://www.fordham.edu/halsall/
"Internet History Sourcebooks are collections of public domain and copy-permitted historical texts presented cleanly (without advertising or excessive layout) for educational use." Excellent for Ancient, Medieva, and Modern history research. Special sourcebooks on topics: African, east Asian, Indian, Islamic, Jewish, Women, Global, Science, GLTB.

Sallie Bingham Center for Women's History and Culture: Women's Liberation Movement, African American Women, Civil War Women
http://library.duke.edu/rubenstein/bingham/guides/digital.html
Diaries, letters, photographs and prints relating to the lives of women.

Teaching Politics: Images of American Political History
http://bill.ballpaul.net/iaph/main.php
A collection of over 500 public domain images, originally developed to support teaching of American political thought.

The Valley of the Shadow: Two Communities in the American Civil War
http://valley.lib.virginia.edu/
Valley of the Shadow Project takes two communities, one Northern and one Southern, through the American Civil War. It is an archive of newspapers, letters, diaries, photographs, maps, church records, population census, agricultural census, and military records.

WAAW: Women Artists of the American West
http://www.cla.purdue.edu/waaw/
Although this is actually an online course, it offers resources for the study of women, art, the west and the Native American culture.

Women and Social Movements in the United States, 1600-2000
http://womhist.alexanderstreet.com/projectmap.htm
Extensive collection, searchable.