There are a lot of different overlays as well as older versions available. I especially recommend the 'Dufour Map' and the 'Siegfried Map' from the 19th century, the earliest official maps of the country.
Wow, thanks! I've been using the SwissMobility maps, which is mostly using the same data, but this is way more slick (and faster). Check out the embedding options! That's really cool.
http://map.geo.admin.ch/
There are a lot of different overlays as well as older versions available. I especially recommend the 'Dufour Map' and the 'Siegfried Map' from the 19th century, the earliest official maps of the country.