The European Space Agency launched a new tool for visualizing Earth. It’s called MIRAVI which stands for Meris Image Rapid Visualization and it uses the world’s largest Earth Observation satellite, Envisat. The site is very nice with a very good interface that uses AJAX and Flash.
NASA also offers images of Earth with it’s Blue Marble project with the resolution of 500sq m/pixel. You can download the data or view it with Blue Marble Navigator or with Nasa World Wind (which uses other sources besides Blue Marble).