I'm still in the middle of my series about "Pulling PPC Levers," but in the interest of sharing some information on the organic/SEO side, I read a great summary recently of how you can optimize one web page for both the singular and plural versions of a search term.  For example, if you sell EDI services, you may want to target both "EDI service" and "EDI services."  One option is to optimize two web pages -- one for each version of the term.

 But if you prefer to squeeze them into one page, it can be done without reading awkwardly.  This article from Search Engine Land explains how to do so in terms of the web page's title tags.