See AutomaticLinkBack.
The Google backlink service lists all pages in its database that refer to a current page
'Example:
To list all its indexed pages that refer to the RecentChanges of WardsWiki / MeatBall, prefix their URLs in the following way:
http://www.google.com/search?q=link:http://c2.com/cgi/wiki?RecentChanges
http://www.google.com/search?q=link:http://www.usemod.com/cgi-bin/mb.pl?RecentChanges
also you can just search on google like this link:siteurl this will show you the external link of that website [Google Backlinks]
The CritLink WebAnnotation tool shows BackLinks with each page.
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.
OddMuse includes this feature. See OddMuse:Automatic_Link_Back.