Technical reports describe the progress and outcomes of a research project, sometimes including recommendations. Technical reports are usually submitted to the agency that funded the research. Some other useful documents are issued by or for governments and may be required by laws or regulations, for example the Biological Opinions that describe possible adverse effects on U.S. endangered species. They are a great source of technical information. "Gray Literature" is made up of significant material (reports, dissertations, etc.) not published by a commercial publisher
Patents are a great source for technical information. They have a very complete description of the device, substance, or process being patented. The easiest way to find them is in the Google Patent Search.
The Tools control at the top of the Google results lets you limit by date, patent office (=country), or other characteristics.
Millions of images are available for you to use in your class papers or presentations.
Tech reports can require a lot of deep searching, but Google Scholar makes it easier, because it includes them along with journal articles and books.
See Setting up Google Scholar on Your Computer for instructions on making Google recognize Chemeketa's journal articles.
Some of the databases on the Databases on the Web are good sources for technical reports, government reports, and preprints in a particular subject. Here are a few of many. For information about these and others, please see Databases on the Web.