GeoSmart is a plugin for WordPress which allows you to determine where in the world the people who comment on your posts are located based on their IP addresses. GeoSmart can automatically add the location information of each comment author to the metadata of each comment as well as generate a map showing the global location distribution of the comment authors for each post on your blog. To display these maps you will need to obtain a Google Maps API Key.
Plugin Homepage: http://www.samuelfolkes.com/projects/geosmart/
Download Link: http://downloads.wordpress.org/plugin/geosmart.zip