If you're in the unenviable position of having to traverse the country by bus or train, you better make sure this map is on your phone.
Put together by the American Intercity Bus Riders Association, it shows you all the bus and Amtrak routes that span the United States. Click "enlarge" to embiggen and you'll find out that it is really, really quite detailed. You can download it as a PDF here. [American Intercity Bus Riders Association via Flowing Data]