I just learned that all of the excellent Swiss Topo maps are available online, see this part of the Switzerland Mobility website. You can zoom in all the way down to 1:25,000 (i.e., you can see every building and small hiking path marked) and can print sections of the map at any scale you choose. All of Switzerland is included, plus the closer parts of the surrounding countries. You can also add overlays of the national cycling, hiking, and other routes.

I'm surprised that this is all available for free, normally you have to pay for this kind of information. I've previously used the SwissGeo website for this purpose, but this Switzerland Mobility one shows much more of the map at a time, the control interface is much better, and the printing function seems great. It still might not be a good idea to use this to replace a real, paper map, but I've used the SwissGeo website in the past to add more detail to sections of my 1:100,000 maps where I was planning to hike and wanted to know where all of the trails were, rather than just the major ones marked on my larger-scale map.

If anyone knows of more websites with topographic maps (i.e., that show contours, altitudes, and hiking trails), then please post the links here. Of course, the Google maps satellite and terrain views are also nice to look at, but they do not give the detailed information that a topographical map does.