That was Milgram's, yes. Zimbardo's was the one where he told half of his subjects they were jailers, and the other half were prisoners, and had them roleplay it for a week. He sat back and watched as the jailers got more and more abusive.
I just want to add a bit after reading about this experiment from a number of sources. During the time many people were asking why did acts often seen in prison happen so often (guards abusing their powers, using violence, prisoners being so depressed, not adjusting to society easily, etc.) and the answer was often given that with such deranged "animals" being kept of course the result was as crazy an environment as was observed. This experiment was sort of a response, though they never imagined how far this would go.
See, they got college students (all would have an education) and screened them down to 21 people (who all had extremely similar psyches and were least likely to become insane for whatever reason) (Forgot to mention they would be paid to do this). Then,
randomly, 11 were selected as guards and 10 as prisoners (it might have been 10 and 11, I don't remember for sure) to see once and for all if it was their psyche that had any effect on how they behaved or if it was the work environment itself causing such results.
The experiment was supposed to go on for two weeks I believed, but was shut down on the 6th. The guards had begun to use extreme violence and be very commanding. Prisoners didn't seem to realize they were being paid to do this, even when reminded they could leave at any time they refused, even when told they would still keep their pay thus far. They were very submissive. Even the man conducting the operation (which I can't remember if it was Zimbardo completely or he had a second guy doing this) who was acting as the warden of the prison was told by his wife that he was taking this way too far.
Zimbardo and others conducting the experiment were worried that any permanent psychological damage had occured. Honestly, they never expected anything of this magnituded to happen or they never would have committed to this project. All those in the study were followed up periodically for years and years to come. No permanent psychological damage was noted whatsoever. Most commented that as soon as they went back to their normal lives they went back to acting normally and that they just think about this past experiment as a lesson learnt.
Makes you kind of think of the reply the bush administration gave after the fiasco with the Iraqi prisoners right? Here's an examples article I looked up:
http://www.cbsnews.com/stories/2004/04/27/60II/main614063.shtml
A quote from it: “So what would I tell the people of Iraq? This is wrong. This is reprehensible. But this is not representative of the 150,000 soldiers that are over here,” adds Kimmitt. “I'd say the same thing to the American people... Don't judge your army based on the actions of a few."
Were these just the black sheep of the American family or was there more to it?