FREE WordPress Plugins by Robert
RDP Wiki Embed
RDP Wiki Embed will pull content from any MediaWiki website (such as wikipedia.org). It strips and re-formats the content, allowing you to supply some arguments to dictate how this works.
RDP Wiki Embed can also look for all links to wiki sites listed in the Security section and force the content on the current page to be replaced with the content found at the wiki site when the link is clicked. Visitors will be able to read wiki content without leaving your site.