To understand the importance of theory, to understand the importance of grounding research ideas in past research, or to help students write introductions, you could have the students read the introduction of any article listed below. However, if you want to stress theory, you might want to start with
Neat series of studies on incidental similarity and compliance. Note that (a) only Study 1 is a simple experiment (the others are three-group experiments) and note that (b) the researchers use chi-square, rather than t tests, to analyze the data from Study 1.
The three-group experiment that helped launch cognitive dissonance theory. The handout points out that writing standards, ethical standards, and statistical standards (the authors used t tests to analyze their data) are different now than they were in 1959).