Primary sources can include: artifacts, audio recordings, diaries, internet communication, interview, letters, peer-reviewed journal articles, original documents, patents, photos, proceedings, records of organizations, speeches, videos, survey results, works of art, web sites.
Secondary sources are sources and information that is produced "after the fact" and are often interpretive in nature. Examples of secondary sources include: bibliographies, biographies, criticisms, commentaries, dictionaries, encyclopedias, histories, journal articles, monographs (except fiction and autobiographies), textbooks, websites.
Tertiary sources combine elements of primary and secondary sources. Examples of tertiary sources include: almanacs, bibliographies, dictionaries, encyclopedias, factbooks, guidebooks, manuals, textbooks.
Do you notice that some items can be considered primary, secondary, and tertiary? Sometimes it is diffcult to determine what is original and what is an interpretation or distillation of an original work.
Here is a great summary from University of Maryland that compares the three types of sources:
Other sources for evaluating primary source materials can be found here: