Lisa Wells' images illustrating principles of geomorphology. There are some great shots from South America, good arid lands geomorph pics. The Earthshots page from the USGS has several case examples of remote sensing and GIS applications for monitoring environmental change. NASA's Earth Observatory. A great resource for discussions on our rapidly changing earth system.
Topics range from drought to fire to climate change.
There is an archive of articles. Another NASA site. Good resource for viewing geomorphic processes from a shuttle's perspective. A companion site to the above. You can search for shuttle imagery of a particular place or region on the earth.