The Christian Science Monitor has a good short survey on attempts to describe and codify human facial expression of emotions. 

In the 4th century BC Aristotle came up with what he thought were the 14 irreducible emotions: Anger, Calm, Friendship, Enmity, Fear, Confidence, Shame, Shamelessness, Kindness, Pity, Indignation, Envy, Emulation, and Contempt.