There are a variety of tricks crop-circle makers use that are really simple, but produce results that can seem freaky. For example, bent but unbroken stalks can be made by attatching a board to your foot, and pushing the stalks sideways, then down.
Here is a bit on some MIT guys who make them. http://web.mit.edu/newsoffice/tt/2002/oct09/crops.html
I note that the comparably simple design that the MIT guys made has a path into it from outside the field. It also doesn't say how long they took to make it or if they did it in the dead of night. It shows a pic of them in broad daylight. The obvious conclusion here is that 'real' crop circle makers are far more sophisticated than MIT juniors in aeronautics and astronautics, have more technical resources available to them and have spread their techniques of sowing iron molecules and seed deformation to circle makers around the world without letting word of it get out of their inner sanctum of pranksters.
Does our premiere school of science have that far to catch up with the jokesters of the world? Or is this what serious engineering grads do for kicks once they have that Masters Degree in hand?