Gvisit is pretty neat. It’s a google maps hack that tracks website visitors and shows you, on a world map, where the visitor is located geographically. It’s free, although only the last 20 visitors are shown if you don’t donate. My Gvisit visitor log is here.
It’s really easy to setup also. All you do is enter your site name and URL. After that you’ll be given a little snippet of code to put on your site, I just put it in my header.
I’d like to see Google itself do something like this for site operators. They would be able to store lots more data for each site served. It’s not really of much use, but it is neat. Geourl is being used for something similar.