Flare :: data visualization for the web (in flash)

"Flare is an ActionScript library for creating visualizations that run in the Adobe Flash Player. From basic charts and graphs to complex interactive graphics, the toolkit supports data management, visual encoding, animation, and interaction techniques. Flare features a modular design that lets developers create customized visualization techniques without having to reinvent the wheel.

This latest release is a major update with numerous improvements to simplify the process of creating rich, interactive visualizations."

And to top it off, the library is one of the best written (from a pure coding stand point)

Check it out. http://flare.prefuse.org/