USGS has published a new 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...
Data download: http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/GMTED2010
GRASS GIS processing steps: see here