umbracoStats makes it easy to track a lot of info on visitors and despite all the unique features like tracking logged in users on the site and much more, this post will feature a classic; tracking visitors by country:
Click for large image
This feature is for all versions of umbracoStats (except the light version). You can decide the top number of countries to be displayed and choose to see them in either pie chart or bar format. IP-databases are updated every day, and data is very fast accessed by a central webservice, keeping your installation at a minimum without any maintaince.