General

1. Natural Earth – Raster: Includes various raster images, for example hypsometric tints, land cover, shaded relief.
2. Global Map: A set of  GIS layers covering the whole globe at 1km resolution including: transportation, administrative boundaries, land cover, elevation, drainage, vegetation, land use and population centres.
3. DIVA-GIS Country Data: It includes administrative areas, inland water, roads and railways, elevation, land cover, population and climate. Probably the easiest place to get a simple set of data for a specific country.
4. MapCruzin: GIS site including wide range of data for various areas of the world. Some datasets appears to be of low quality, but others are good.
5. GeoNetwork: GIS site including a wide range of data under various categories.
6. Natural Earth – Vector: It includes data related to coastline, islands, rivers, land, oceans, lakes, glaciated areas .