University of California, Davis
http://psychology.ucdavis.edu/faculty_sites/sommerb/sommerdemo/experiment/types.htm
This site provides an excellent overview for students on the types of experiments, utilizing examples and charts for each.

Yale University Institution for Social and Policy Studies
http://gotv.research.yale.edu/?q=node/49
This site takes students through an actual natural experiment conducted by Krasno and Green in 2006 which tested whether televised presidential ads increase voter turnout. The findings indicated that ads televised in the final days of a campaign have little influence on turnout.

National Bureau of Economic Research
http://www.nber.org/papers/t0170
This website provides an excellent listing of working and published papers which utilize natural and quasi-experiments in economics. These are excellent sources of ideas and examples to help guide student research.

National Center for Technology Innovation
http://www.nationaltechcenter.org/index.php/products/at-research-matters/quasi-experimental-study/
This site discusses the value of quasi-experiments in research, providing elements of conducting this type of study, along with examples.