WWW FAQs: Why do my MP3 files sound bad in Flash Player?
Explains the sampling rate issues with audio in Flash and provides step-by-step directions to correct it using Audacity and LAME
Ajax Animator Open Source Flash
Web-based open source application for creating animations. Allows for the creation of multiple layers and uses a timeline. Not much documentation or support since it's early in development, but looks like it's worth playing with if you don't have the budget for Flash and do have some time.
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.