I always loved these homunculi drawings in intro psych and neuro books. These sculptures from the London Natural History Museum are even better!
click picture for much much larger image.
And finally if you have no idea what the heck is going on here. Wikipedia has a good description of the homunculus.
[edit by Sandra - in keeping with our new R-rating, see the NSFW image of a proposed revision involving the penis. Read more here. Oh, and I find it curious/sexist that I can't find an image representing a female homunculus...]