In accordance with the Columbia Guide to Online Style (Columbia University Press) the basic format for citing electronic publications is:
Author's Last Name, First Initial. "Title of Work." _Title_of_Complete_Work_. [protocol and address] [path] (date of message or visit).
Specific Examples
Citing a page on the GrainGenes Webserver
Holland, J. "Coefficients-of-parentage of early and midseason oat cultivars". In _GrainGenes_. http://wheat.pw.usda.gov/ggpages/oatCoP.html (17 Nov. 2000).