A new version of Flare, the data visualization toolkit for Actionscript (which means it runs in Flash), was just released yesterday with a number of major improvements from the previous version. The toolkit was created and is maintained by the UC Berkeley Visualization Lab and was one of the first bits of Actionscript that I got my hands on. The effort-to-output ratio was pretty satisfying, so if you want to learn Acitonscript for data visualization, check out Flare. The tutorial is a good place to start.
Here are some sample applications created with Flare: