Items such as campaign buttons, posters, event flyers, and other materials can also serve as sources for information and analysis. This is one reason why museum display artifacts to help bring history to life. Added information and insights might be conveyed through these materials.
Interviews and audio recordings, either collected by others or done by the researcher, can serve as a useful resource. They can be especially relevant for topics that might have better documentation through oral tradition and spoken word. These are increasingly available especially for 20th century topics due to the increasing availability of recording equipment. Earlier speeches and interviews are often primarily accessed through transcripts but a growing number are available with both audio and transcription options.
EXAMPLE: Oral Histories of the American South (part of UNC-CH's Documenting the American South): http://docsouth.unc.edu/sohp/