I heard a lot before about the Stanford Prison Experiment (read about it in Wikipedia). In short, it was an experiment conducted in 1971 where a group of students “played” the roles of both guards and prisoners in a prison. The experiment was supposed to last 2 weeks, but instead was stopped after 6 days because of concern for the prisoners’ and guards’ health.
Someone posted a 50 minute TV program about the experiment, including amazing videos from the experiment, showing the behavior of both prisoners and guards. (via Digg)