Original Research Articles -- Peer-reviewed articles written by those who conducted the research.
Conference Papers or Proceedings -- Pre peer-reviewed articles and oral presentations created as a way to test out new ideas and research.
Correspondence -- Exchanges of letters, e-mails, or other forms of written messages.
Dissertations -- Lengthy treatise usually written by a candidate for the doctoral degree at a university.
Diaries -- A daily record of events or measurable phenomena.
Interviews -- A conversation in which facts or statements are elicited from an individual.
Surveys -- A gathering of a sample of data or opinions considered to be representative of a whole.
Theses -- A dissertation advancing an original point of view as a result of research, esp. as a requirement for an academic degree.
Experimental data -- Resultant data relating to, derived from, or founded upon an experiment. Academic Press Dictionary
Laboratory notes -- Notes documenting a researcher's hypotheses, experiments, and initial analysis or interpretation of their experiments.
Technical Reports -- a document that describes the process, progress, or results of technical or scientific research or the state of a technical or scientific research problem. wikipedia
Patents -- Grants made by a government that gives a creator exclusive rights to make, use, and sell that invention for a set period of time.
Photographs -- That which is worth a thousand words.