For those interested in animation and 3D, I recommend two tools that complement Flash very well.
For 3D authoring with Flash, I recommend Swift 3D:
Swift 3D is the only 3D application to directly integrate with Adobe Flash and provides unrivaled vector rendering quality and output style options. Swift 3D’s toolset and interface allow anyone to quickly create 3D content while providing a full set of advanced tools to grow into. (…) Swift 3D MAX and Swift 3D LW are plug-ins to 3ds max and LightWave 3D, providing users of these high-end 3D programs with the same export options that Swift 3D provides.
If you’re interested in more advanced animation options than the ones Flash provides, I recommend Toon Boom Studio:
Toon Boom Studio V3.5 is ideal for individuals looking for an all-in-one animation solution, from drawing digitally, scanning hand-drawn animations, seamlessly importing existing artwork, to lip-syncing the animation, setting up the action in a 3D space and publishing animation projects for TV, HDTV, the Web and iPod