Space Shuttle Images - a clickable world map with space shuttle images of various locations.
Space Shuttle Images - includes clouds from space, plate tectonics, volcanoes, etc.
Earth From Space - more space shuttle pictures but grouped into categories such as cities, earth landscapes, hurricanes, geographic regions, etc.
Space Radar Images Of Earth - another large collection of images grouped into categories which include cities, ecology & agriculture, rivers, volcanoes, snow, ice & glaciers.
Terraserver - a Microsoft site which you will either love or hate! The concept is wonderful - declassified high resolution images from Russian spy satellites which you can zoom in on right down to fields and individual buildings. The site can be busy, slow and awkward to use - try it and see...
Satellite Images of the Earth at Night - from the International Dark-Sky Association who campaign against light pollution, comes this weird and wonderful set of images.
Earth and Moon Viewer - generate a live image based on topography, cloud patterns, etc with current day/night superimposed.
Global Hydrology & Climate Centre - global weather views. Includes visible, infra-red and water vapour images. Areas covered: N.America - GOES satellite, Japan, Australia & Asia - GMS-5 satellite, Europe, Africa & Atlantic - METEOSAT-7 satellite.
Space Science & Engineering Centre - from this site comes one of the best images that I have found on the Internet. These are full-colour global maps showing differences in land and sea temperatures. They make wonderful windows wallpaper images.