USGS has published a newÂ nice data set called the “Global Multi-resolution Terrain Elevation Data 2010” (GMTED2010). It is offered at three different resolutions (approximately 1,000, 500, and 250 meters).
Example (MEA = mean dataset) Trento – Garda Lake – Verona area (Northern Italy):
The 250m product looks quite smooth -a nice new DEM product…
GRASS GIS processing steps: see here