Some interesting stuff on crop circles - if you search for it. The references at the end of the Wikipedia entry are useful.
One researcher, Northcote, from a university in Australia did an analysis of the locations of crop circles in England in 2002. He noted that there was a cluster of circles around Avebury, most other circles appeared to be fairly close to areas of large population, and that the presence of major roads, such as the M1 and A1 appeared to be important factors in location.
It would seem bizarre that aliens would require the AA Road Atlas to find their way around.
Another thought has occurred to me. When do crop circles appear? Do the occur in winter? If not, why not? Do they occur in spring or autumn? If not, why not? Do they occur in anything much other than valuable farmed crops? If not, why not? Can we conclude from this that aliens are concerned about our diet?
A principle in scientific analysis is that of parsimony: if there are more than one explanations of a phenomenon, then consider the the most parsimonious explanation to be the most likely until it is demonstrated to be inappropriate - Occam's Razor is a version of this.
Which is likely to be the more parsimonious explanation for this non-randomly distributed, seasonal, crop-selective phenomenon? Hoaxers or aliens?