The Google backlink service lists all pages in its database that refer to a current page
also you can just search on google like this link:siteurl this will show you the external link of that website [Google Backlinks]
To save the user keystrokes a system link on each Wiki page to its external referents would come in handy. It could help to increase the link density between different Wikis. The script extension has to filter out all internal backlinks.