A longer list along the lines of Colin Gerber's answer. My favorite is the Robbers Cave experiment which replicated the conditions of Golding's Lord of the Flies, and validated his literary intuitions about how things would go.
http://brainz.org/ten-most-revea...

Among the more shocking revelations on the purely physical side, for me personally (can't recall references/citations):

1. Semi-starvation extends lifespan (I think this has only been verified in rats)
2. Separated-at-birth twins show bizarrely specific behavioral similarities and personality quirks, despite being raised apart
3. People with specific sorts of brain damage completely lose the ability to make up long-term memory but still can make up apparently coherent narratives to desperately keep up with events and make seeming sense of their lives, even though it is clear to others that they are messed up (this is called confabulation and is described in Oliver Sacks' The Man Who Mistook His Wife for a Hat)
4. The ability to draw photo-realistically is natural. Drawing badly is an effect of conceptual and logical ways of seeing. So learning drawing is basically unlearning (also in Sacks' books).
5. There is actually a physical meaning to seeing the whole versus seeing the parts. In the title essay in Sacks' book, a guy with brain damage could see a rose in terms of platonic terms but not recognize it as a rose (i.e. he saw it as an uneven sphere on top of a narrow cylinder). And as the title says, he mistook his wife for a hat.
6. Your brain makes up memories and even perceptions so that they make "sense" not as they are. This goes down to very raw, physical perceptions... your sensory experience gets "edited" at very very low, subconscious levels.
7. Your experience of time passing literally speeds up or slows down based on emotional and physical state (running a fever changes your perception of time for example, you'll guess that intervals of time are longer than than you would judge them to be at a normal body temperature).