Since the Serpent is the symbol of our own order, I thought it would be good to begin a discussion of the Serpent as a symbol in various religions and cultures.
To begin with, the most obvious example is, of course, the Genesis Serpent. After being warned that if they eat from the Tree of Knowledge of Good and Evil they will "surely die," the serpent tells Eve (or Chava, as I prefer the Hebrew names) that she will not die, but rather that they will become like god, and god does not wish that to happen. Sure enough, once the fruit is eaten, the Angel says "Now he is like us." In this, arguably the central myth of the Judeo-Christian mythology, the Serpent tells the truth, and God lies. Genesis makes no attempt to obfuscate it. This makes it clear to me that the Genesis Serpent is not intended to be a stand-in for evil, but rather is used as the Serpent is often used in mythology and symbolism, to represent knowledge and wisdom and, in the case of the Genesis myth, as the supplier of isolate consciousness and self awareness; to place it into our own terms, the guardian of Xeper, and the custodian of the path to godhood.
There are many other examples of the Serpent as a symbol for wisdom. The Caduceus and Rod of Asclepius are two more well known examples.
The Egyptian netjer Wadjet takes the form of a Serpent, and is the protector of Lower Egypt, associated with other netjeru including Bast, Sakhmet, and Mut (the World-Mother). In this role she takes on a solar aspect, as Bast and Sakhmet are Eyes of Ra, but Wadjet is also associated with the eclipsing binary star Algol (meaning "The Demon," appropriately enough), which represents the eye in the severed head of Medusa in the modern constellation Perseus. I've been interested in Wadjet as a stellar netjer for a while and may put together an essay on the subject.
What are some other favorite instances of the Serpent in mythology?