looks like GMTED2010 data  should qualify as DFSG-free global digital
elevation model (GDEM). Resolution is better (7.5arc-seconds) than that
of G.L.O.B.E. (good) and there are no voids to fill.
Package/Makefile to download the data and create a single geotiff:
maybe use it as base below SRTM data
any comments welcome
 Danielson, J.J., and Gesch, D.B., 2011, Global multi-resolution
terrain elevation data 2010 (GMTED2010): U.S. Geological Survey
Open-File Report 2011–1073, 26p.