I attempted to make a crude GSR sensor (Galvanic Skin Response) consisting mainly of a voltage divider, two copper plates, and an analog input.
I used this wiring (source: http://www.instructables.com/id/Stress-Makes-Art-Galvanic-Skin-Response-and-Visual/ )
I can certainly get results from it and at first glance the data looks useful, but it's unclear whether I'm reading what I think I am. I can certainly tell whether there is skin contact, at least. But beyond that it's inconclusive.
I subjected myself to various stimuli (consciously calming my mind, consciously tensing up, jabbing my hand with a screwdriver, hyperventilating, looking at pictures of pretty girls, and things of that nature) with the contacts applied to my skin but was unable to find any useful patterns besides "skin contact yes/no".
More testing and study is needed if time permits.