Twitter Friends Map lets you view the people you follow on a Google Map. Once you connect the map with your Twitter account you can view the locations of all the people you follow on Twitter.
The map includes a novel marker clustering solution. Clusters of your friends are shown by a number within a white circle marker. If you mouse-over the marker it expands to display the profile pictures of your friends.
If you like the map or the marker clustering solution you can view the code on gihub.