I have previously posted about the usefulness of SiteMeter as a free tool to find out how people are finding your blog. They have recently added a feature that displays a map of where your visitors are located. It is free for the last 100 visitors.
This is a great way to demonstrate graphically that open course materials are accessed broadly. Here is a map for my CHEM 243 class. Putting the mouse pointer on top of the dots gives more detailed information.