SRTM: Coverage of the World from North 60° - South 58°
Viewfinders Panoramas: Enhanced datasets for mountain areas on base of public domain datasets (look at the website of this great project for all the data sources).
Radarsat Antarctic Mapping Project: Antarctica
Geobase Canada: Northern Canada (> 60° N)
NED USGD, for Alaska: Alaska
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License: Open Database License (OdBL)
Selected datassets: