Similar search engines

Phil Bradley's site pointed me to similar-site.com, which delivered some very good results when I searched for sites similar to Knowbodies. It gauges "similarity" primarily on the basis of user annotations or tags on websites. It also does a good job of finding sites similar to itself,  while comparable sites -   http://www.similarsites.com/  and web.insuggest.com - performed less impressively.  Also very useful when looking for similar sites is the "similar" option that appears in the Google search results lists, or - for the pro-active - the "related" Google search operator, with syntax related:knowbodies.blogspot.com