GeoNetwork opensource is a Free and Open Source catalog application to manage spatially referenced resources. It provides powerfull metadata editing and search functions as well as an embedded interactive web map viewer.

The UN Food and Agriculture Organization's GeoNetwork spatial data catalogue, provides agricultural information to decision-makers, allowing them to access satellite imagery, interactive maps and spatial databases from FAO, WFP, CGIAR and others. This new version of GeoNetwork is faster and more reliable than the previous one. In addition, several other UN agencies have joined the network, thus adding an impressive amount of valuable UN system-wide geospatial information.

The Integrated CEOS European Data Server (ICEDS) uses Open Geospatial Consortium technologies for map and data serving; serve datasets for Europe and Africa, particularly Landsat TM and Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data; and others.

The Earth Science Data Interface (ESDI) at the Global Land Cover Facility (University of Maryland-US) provides free access to STRM data, and as a bonus you can download landsat images already aligned to STRM tiles.

Digital Elevation Data for the Entire Globe Now Available on the CGIAR-CSI GeoPortal: The CGIAR-CSI is now able to provide "Hole-filled seamless SRTM 90mDigital Elevation Data" for almost the entire globe for download. The SRTM DEM's have a resolution of 90m, and are provided in 5 deg x 5 deg tiles for easy download and use. These are available in both ArcInfo ASCII and GeoTiff format to facilitate ease of use. Data can be downloaded using a browser or directly from the ftp site.

The NOAA's National Geophysical Data Center (NGDC) offers gridded global relief data and images in multiple resolutions. Two-minute gridded global relief for both ocean and land areas (combined bathymetry and topography) are available in the ETOPO2 database. 30-second gridded land topography are available from the Global Land One-km Base Elevation (GLOBE) Project data files. Historic 5-minute gridded global relief data (ETOPO5 or TerrainBase) have been superseded by ETOPO2, but are still available.

NASA has released version 2 of the Shuttle Radar Topography Mission digital topographic data (also known as the "finished" version). Version 2 is the result of a substantial editing effort by the National Geospatial Intelligence Agency and exhibits well-defined water bodies and coastlines and the absence of spikes and wells (single pixel errors), although some areas of missing data ('voids') are still present. The Version 2 directory also contains the vector coastline mask derived by NGA during the editing, called the SRTM Water Body Data (SWBD), in ESRI Shapefile format. The data may be obtained by anonymous ftp to: ftp://e0srp01u.ecs.nasa.gov and moving to the directory srtm where both version 1 and version 2 directories may be found. Please read the appropriate documentation, also found in the directories.

Viewfinder Panorama has an extensive collection of digital elevation models, panoramas and other mountain related information that is freely available for use, provided permission and credit is given.

GeoNetwork OpenSource is a web based Geographic Metadata Catalogue System developed by FAO-UN, WFP-UN and UNEP. The system implements the ISO19115 Geographic Metadata and ISO 23950 (Z39.50) standards. Furthermore it provides an OGC-WMS client application InterMap OpenSource and integrates the Deegree OGC Web Map Server in its full installer version, including sample data.

TUNEP's GRID-Arendal's Online GIS and Map and Graphics Database offers a free collection of maps, graphics and diagrams, illustrating environmental issues. These images are produced using desktop publication software such as Freehand, Adobe Illustrator, CorelDraw , etc.

The GeoCommunity and Digital Data Services offers DEM for the USA

Francis T. Koti's "How to make your own DEM -  recommends to simply digitize the contours and use the attached procedures in "ArcGIS" if your area of interest is not that big, and if time is not a constraint.