Question2answer Top Search Adds a widget which lists the top searched content
Has an admin option to choose betwween normal search results and tag search results. Tag Search is given by this plugin: http://www.question2answer.org/qa/52496/tag-search-plugin-free
Plugin requires Event Logger to be turned on.
Styling of the widget can be done via the admin interface.
This is a beta code, using it at your own risk on a production environment.
Plugin would not work if you are using google custom search instead of Q2A search.