Google Earth

Google Earth - A satellite imagery tool

 * http://earth.google.com/

According to Google, Google Earth "...combines the power of Google Search with satellite imagery, maps, terrain and 3D buildings to put the world's geographic information at your fingertips.".

In practice it does allow users to view high quality satellite imagery, free of charge, of a number of topical locales. In particular, it is worthwhile looking at Rome.