Aircraft have altitudes - roads and landscapes have elevations. The reasons you don't see many of the "altimeters" for the dash like we used to have in our old Jeeps is that any modern GPS will give you the elevation by just tapping the vehicle icon. Flattestroute.com as suggested is a good tool. I also find The Mountain Directory (East and West versions) to be very useful. You can also find elevations on Google Earth. Finally, if you are interested in a particular city, just look up that city on Wikipedia. In the little data window over on the right hand side of the Wikipedia page, the elevation will be listed along with the other stats.
Rob