Types of Resources

Primary

Conference proceedings - Scholars and researchers getting together and presenting their latest ideas and findings
Books - Extensive and detailed discussions of a particular topic or set of topics, written by the scholars and researchers who came up with the ideas or discovered the findings.
Journal articles - Brief, specific analyses of particular aspects of a topic, written by the scholars and researchers who came up with the ideas or discovered the findings.
Lab reports - Experiments, observations, etc.
Historical documents - Official papers, maps, treaties, etc.
First-person accounts - Diaries, memoirs, letters, interviews, speeches, oral history
Recordings - audio, video, photographic
Artifacts - manufactured items such as clothing, furniture, tools, buildings, toys, religious objects, architecture of a culture
Newspapers - Some types of articles, e.g. stories on a breaking issue, or journalists reporting the results of their investigations.
Government publications - Census statistics, economic data, court reports, etc.
Internet - Web sites that publish the author's findings or research; e.g. a professor's home page listing research results.
Manuscript collections - Collected writings, notes, letters, diaries, and other unpublished works.
Archives - Records (minutes of meetings, purchase invoices, financial statements, etc.) of an organization (e.g. The Nature Conservancy), institution (e.g. Wesleyan University), business, or other group entity (even the Grateful Dead has an archivist on staff).
Ads/Broadsides - Billboards, magazine inserts, and posters.
Laws, Inventories, Birth/Death certificates, Wills, Photographs

Secondary

Books - Extensive and detailed analyses by scholars providing criticisms, commentaries, and interpretations of primary ideas and findings.
Journal articles - Brief, specific analyses, criticisms, commentaries, and interpretations of particular aspects of primary ideas and findings.
Newspapers - Articles which report on earlier findings, or offer commentary or opinions.
Internet - Web sites that comment on earlier findings or research

Tertiary

Encyclopedias - Articles providing introductory or summary information; coverage can be general (e.g. Encyclopedia Britannica) or subject-specific (e.g. Encyclopedia of Sociology).
Dictionaries - Definitions or brief summaries of terms, ideas, etc.; coverage can be general (e.g. Webster's, Random House) or subject-specific (e.g. Dictionary of Cell Biology).
Almanacs - Good for concise factual information, e.g. statistics, lists
Directories - Lists of people or organizations, with addresses, affiliations, etc.; useful guides to finding primary source material
Atlases - Maps of population, economic, historical, political, geological, biological, climatological, etc. information.
Indexes - Lists of sources on a subject or set of subjects; once you have some key terms for your topic, use indexes to find secondary and primary sources.