Webpages that appear to have no author usually have a corporate author that takes responsibility for the content. If no one at all takes responsibility for the content, then you should be very, very cautious about citing it, but if there truly is no author, then start the citation with the title of the webpage.
Template:
Title of webpage. (2010). Retrieved from Site Name website: htttp://xxxxxxxx
Example:
New child vaccine gets funding boost. (2001). Retrieved March 21, 2001, from http://news.ninemsn.com.au/healthstory_13178.asp
Note that Wikipedia is a special case because it is structured as an online encyclopedia and so is cited as one.