Macromedia Flash - The one that started it all and the industry standard Flash editor. Quite a steep learning curve but tons of possibilities.

Swish - Flash animator with a ton of inbuilt effects. Highly configurable and saves you hours of manual work.

Flash Toolset - Stuffed with advanced features, most notably saving .swf from IE and extracting shapes, images and movie clips from .swf files

De Flash - A tool which allows you to decompile .swf files and extract all elements including actionscript.