It is surprising how crop circles are still carried around as mysterious phenomena. Basic google searches seem to landup with a concoction of pages that dont always lead to a straight (and skeptic) answer. So, i pulled a good starter on the issue.
These notes have links to several interesting references and other work.
For those new to this topic (really?) or in need of a context, there are a couple of articles on the subject:
An Aug-2002 article Weird science: Circular logic with a followup link to a little more recent (and aptly named for July-2004) The fellowship of the rings.