For some of the most amazing fireworks extensions, check this place out. I had the distinct pleasure of meeting one of the founders of phireworx at TODCON, Steven Grosvenor. He will amaze you with his knowledge of the Fireworks API, and excellent design skills. They've got some cool stuff in the works so keep an eye out.
If you do any sort of design work with Fireworks, Phireworx is the place to be!