TrailTopo is a site dedicated to providing free topographic maps. It uses services such as Google Maps API, MyTopo, and CalTopo. You can generate U.S. maps with a click of a button, just scroll to the place you want a map for and generate nicely detailed maps. Keep in mind that TrailTopo currently does not generate topo maps outside of the United States but does display terrain mode for the rest of the world.
Mid 2018 I plan on improving the user interface, fixing the mobile view with CalTopo (hill shading issue), adding a full documentation explaining how to use the KML/GPX import feature as well as making things more mobile friendly. As time permits eventually I want to integrate Canadian maps, OpenStreetMaps, and user submitted content. - Josh Lewis