Whirlwind Theory
This is the oldest explanation of crop circles (remember the "Devil Winds" from the Early Encounters page?). The theory basically states that whirlwinds or tornados form and swirl over fields, causing the crops to bend over.
This theory is discredited by most for its obvious flaws. One major critique is simply that no tornados in the wheatfields of Kansas or anywhere else in the world have ever created anything that looks remotely close to a crop circle. This theory is essentially the stand-by theory for those who do not wish to get involved in the crop circle debate.
Now for exciting stuff; on to the music theory.