Resources for lesson plans don’t include just the lesson plans themselves, of course. The plan is the outline, the skeleton. The actual lesson involves getting students to interact with the information in the plan’s focus. Teachers don’t make up the informaton for the students, and teachers definitely don’t want the students to make up the stuff they write (well, there is always creative writing…)
The Internet is increasingly providing access to solid information. Not all of it is free to copy, but much of it is. Wikipedia’s current article count is 2,779,000+ for the English version. The content is licensed with the GNU Free Documentation License. That is the equivalent of the free software license and encourages document reuse with the same freedoms as the GPL offers for software. That means you, the teacher, can incorporate an article from Wikipedia in your lesson plan, copying it verbatim, printing and distributing it to your classes. What’s more, you can modify the document, adding specifics for your lesson. You do NOT need to worry about breaking any laws. The license is education friendly, unlike standard copyright license which limits your use of material to immediate, short-term, excerpt from the source. With standard copyrighted works, you are stealing from the publisher and author if you duplicate from a book or workbook for more than one class and certainly if you use it more than one year.
Another issue is primary source. Wikipedia isn’t designed to present original research. The submission rules speak against that sort of writing. The idea is to write an article with references that back up the statements in the article. It is reference material in the same way that traditional encyclopedias are.
Getting primary source material is also easier than ever because of the Internet. There are several initiatives designed to present accessible primary source material.
The Library of Congress has an ever-growing Web accessible digital conversion of its massive paper collection. Most social studies/history teachers are aware of and recommend students use the Library of Congress American Memories site.
Scientific research is commonly published in peer reviewed journals. The peer review is designed to ensure quality of research reports, keeping wild claims from being made, demanding high levels of proof be presented before a research article gets published. Unfortunately, the traditional scientific journals are also expensive to produce. They don’t have advertising support, for example. Most high schools don’t have copies, either.
The Internet gives a new publishing opportunity, and recently “open access” journals have begun to appear. These are the same peer reviewed journals, but not limited to paper and the back room stacks of university libraries.
Check out the Directory of Open Access Journals. It isn’t just for science classes, either. History, the arts, psychology, language study, they are all represented.