I Came, I Saw, I Learned...: Flash CS4: Inverse Kinematics and ActionScript 3.0
Very cool stuff in Flash CS4. Create a "bone structure" with joints that move realistically. I have no idea how I'd use it, but the demos are worth checking out.
Blog posts
Swftools.com - Flash tools, utilities, applications, components
Directory of tools that do at least some of what Flash can do or that work with Flash--presentation tools, quiz tools, PowerPoint to Flash converters, ActionScript editors, etc. Most have free demos; not many open source options in this area.