Flash, and Flex in particular, has a solid set of tools available ata visualization. When I found that the USGS provided realtime earthquake data as csv files I couldn't resist building a viewer. It's based on a traffic map by Nathan at Flowing Data
What is It
The map polls data from the USGS's realtime earthquake data stream. The resulting data is presented as a map with dots representing earthquakes and a 'seismograph' style chart below. You can choose to view data from the previous week, current day or just the last hour.
How it's Built
The viewer is built completely in ActionScript using the Flex toolkit and the Flex Builder development environment. The scrolling maps are all done with Modest Maps. There is some minor glue code to pull the data from the USGS web page and csvlib is used to parse the results.
There are still a lot of user interaction features that would be nice to have, but the basics are all there.
Why not use Google Maps API?