The USGS has global DEM data at several resolution levels: 30-arc-second (1 kilometer), 15-arc-second (450 meters), and 7.5-arc-second (225 meters). The GMTED2010 dataset with multiple resolution levels replaces a former version called GTOPO30, which only had the resolution level of 30-arc-second (1 kilometer). These data have been collected from a variety of sources using aggregation methods. These datasets are best used for working at the continental scale and with very large regions.
The science teams at the NASA Jet Propulsion Lab (JPL) and Japan’s Ministry of Economy, Trade, and Industry (METI) used the ASTER sensor onboard the Terra satellite to produce 30 m resolution elevation data. These data cover 99% of the land surface from 83° north latitude to 83° south latitude. Version 2 of these data was released in October 2011 and is a significant improvement over the initial data release. You can view the latest information about these data at the USGS LP DAAC
In February of 2000 the Space Shuttle mapped most of the land surfaces of the Earth, from 60° north to 56° south, to create the highest resolution global elevation dataset available to date. Global data were released at a 3 arc-second (~90 m) resolution. Data covering the United States were also released at a 1 arc-second (~30 m) resolution. The Version 1 data had many data voids and irregular water surfaces and coastlines.
The National Map is the primary source of the National Elevation Dataset (NED) data of the U.S. at: http://nationalmap.gov/viewer.html.. When you first visit this site you should read the directions for downloading data from the National Map Viewer before searching for data.
Digital elevation data can now be obtained for any place on the Earth, at several resolutions. This document will discuss the major sources for reliable and freely available DEM data. In order to choose the right source for DEM data, there are two main criteria to consider: geographical region of interest and spatial resolution. Below is a table that summarizes the DEM data sources that should be of interest to you.