Flash
I've used Flash to create splash pages and banners for clients, and from time to time I'll indulge myself in animation projects just for Fun, but primarily I find Flash useful when it comes to deploying Video. You can encode and convert other video formats to Flash Video (FLV) which is the preferred format for streaming over the web, and then with the Flash Authoring environment you can easily create your own custom video players.
Below are some examples of things I've done with Flash >>>
