OpenTopoMap is a topographic map out of data from OpenStreetMap and SRTM.
The main OpenTopoMap is a online rendered raster map. It can be used with the web interface on https://opentopomap.org, which gives you nice features like a search function or loading your gpx tracks. Futhermore, OpenTopoMap can be included into other applications. See https://opentopomap.org/about#verwendung for information on usage and license.
The online renderer is based on Mapnik. All necessary files are available to build your own OpenTopoMap server.
Since summer 2014 there is a Garmin edition of the OpenTopoMap. They can be downloaded from http://garmin.opentopomap.org. Here are some screenshots: