This one's not a DEM, but is quite interesting: http://gw.marketingden.com/planets/earth.html Colour, bump (possibly can be used as a DEM, and it has various resolutions), specular of the surface, plus a hi-res map of the clouds. The guy also has maps of other planets. JPL and CalTech have something, too: http://lagesi.caltech.edu/ go to data. No direct link, because the site is framed. Finally, NASA has lots of stuff: http://earthsciencesportal.gsfc.nasa.gov/ Sorry I couldn't be of specific help.

-- erlik