Have you checked http://edc.usgs.gov/? Seems like they have quite a bit of varied data.
But this is likely not very low resolution.
Another source might be: http://serc.carleton.edu/research_education/geopad/topograph...
But this is likely not very low resolution.
Another source might be: http://serc.carleton.edu/research_education/geopad/topograph...