Google released the newest version of its Google Earth product, and has included some terrific new features.
One is the ability to see all of their historic satellite imagery for an area. Most parts of the US seem to go back to 1993, but some go back to the 1940s. You can cycle through each set of images and play them in a loop. A side benefit of this is that you can now see the month and year that the satelitte pictures were taken.
Louisville had about 10 sets going back to 1993. Here is an animation I made of part of our Ohio River waterfront development over time:
And here is a more detailed version of the entire set (click for high resolution):
Another feature is the ability to dive under the ocean and see all of the earth's ocean floors in 3D, thus increasing Earth's coverage by 233%.
You can also now record everything you are doing, including image history, zooming, panning, toggleing features, audio description, etc, and then share this with anyone else throught Google Earth. The recipient can play back what you have demonstrated, including your voice over.
Google LatLong: New in Google Earth 5.0: Historical Imagery