What is a good tool for producing animated sprites?

Has anyone come across a software package that allows you to build animations in a similar way to how you can in Flash (i.e. using techniques such as tweens & bones & easings, etc) and then have the result exported as a sprite sheet?

Answer

You can use Flash, a 3D Tool or even Photoshops animation feature. Then render the frames to images and combine them to a sprite-sheet.

ImageMagick has a great tool for that purpose called montage. Here's a blog post explaining how to use it to create a sprite sheet.