One of our partners in our American Futures project, along with Marketplace radio, is the Esri mapping/geographic-info company of Redlands, California. Here are two interactive maps Esri has recently produced that I think are potential time-sinks of the instructive rather than of the "you'll hate yourself when you spend half an hour this way" variety.
First, a "swipe map" that lets you compare recent rates of county-by-county population growth with the sources of that growth—or decline. You can see the full-screen version of the map here, which also explains its legend. In short, the darker the shade of green on the left side of the map, the faster the population growth. And on the right, a tan color means that migration has been the main source of change—people moving in—while blue means the "natural increase" of births and deaths. A pale color on either side means no growth/no change.
Click the words "Hide Intro" when you first see the map, to get a view in which you can pan around and zoom in or out. Don't click on either "Data" or "Legend" — or, if you do, click back on "Map" to get the real display. Again, darker green is faster growth, and tan is people moving in. If you forget, just look at North Dakota.