The major search engines, i.e. Google, Microsoft's Bing and Yahoo have agreed on a standard tag that every web page should use to tell these engines what is its preferred version. This is called the canonical URL of a page, nicely explained in this article at Google Webmaster Tools Central Blog. The meta-tag should be added at the head section of your HTML page:

<link rel="canonical" href="http://www.example.com/content/title_of_your_story_or_page_here" />