I would love to see one, and to firetwirl in one would be magic. Personally I think the most likely explanation is that it's earth's energies. The closest thing to a crop cicle I've seen was a man-made pentagram-mandala about 4 metres in diameter, made up of candles, incense, crystals, various geometric shapes and all kinds of spiritual ornaments like little buddhas. And believe me, it had a really strong energy, really crisp, clean and refreshing... mmmmm.
I can only imagine what it would feel like to be in a crop circle.