These local Special Collections/archival collections are of particular interest for African-American history:
Auburn Avenue Research Library on African-American Culture and History
GSU Library Special Collections and Archives
Emory University's Manuscript, Archives and Rare Book Library (MARBL)
Archives and Special Collections, Robert W. Woodruff Library, Atlanta University Center
Atlanta History Center Archives (Kenan Research Center)
Hargrett Rare Book and Manuscript Library of the University of Georgia
ArchiveGrid is a freely available site from OCLC which includes nearly two million archival material descriptions from repositories in the US, including records from WorldCat and finding aids harvested from the web.
If you have questions about finding aids or an archives' holdings, look for contact information and contact the archives directly. Archivists know their collections well and can help you learn more about a collection, whether you can order reproductions of materials, etc.
If you are planning to visit an archives, it's best to contact the archives directly before you visit, to learn about registration procedures and other rules the archives may have for using their resources.
For more information about doing archival research, please see our Archival Research guide!