Earthquake Heat Map
There are a lot of Google Maps mashups that use USGS data to show recent earthquakes on a global map. Earthquake Heat Map is an earthquake map that stands out from the crowd because of its very cool heat map visualisation of the USGS earthquake data.
Using the map it is possible to view global heat maps for earthquakes over 2.5 magnitude in the last day, for the last week or earthquakes of over magnitude 5 in the last week.
If you like the map then you will also be interested in the tutorial Creating Map Overlays with the Google Maps API for Flash. The tutorial helps explain how to create an overlay for Google Maps using the Google Maps for Flash API.