NASA
Nasa: Earth Observatory
The purpose of NASA's Earth Observatory is to provide new satellite imagery and scientific information about our home planet to the public. The focus is on Earth's climate and environmental change.
American Geosciences Institute
American Geosciences Institute: Earth Science Week: Exploring Change With Gis
Gives an overview of how Geographic Information Systems technology is used to monitor changes in conditions on the Earth. Provides a link to the website with lessons on using GIS. (Due to site changes, you may need to search for teachers...
Library of Congress
Loc: Earth as Art: A Landsat Perspective
A really cool site showing Satellite (Landsat 7) images of unique geographical and meteorological phenomena. Images show cloud formations to rainforest devastation.