Everywhere you can get on intercity transit in America, in one map
This map, from the American Intercity Bus Riders Association, attempts to show all the major intercity transit routes in America. It includes Amtrak, Greyhound, and several other bus carriers.
It’s probably impossible for this kind of map to be 100% accurate all the time. In all likelihood there are some missing links, and missing carriers. But it’s still quite an impressive undertaking, and a useful tool to bookmark.