This is something that keeps coming up on the forums, so here's a small package that allows end-users to insert flash content from within the editor.
The plugin installs swfobject.js (version 2.2) and an xslt macro that takes the follow parameters
This macro inserts a script tag just before the div to be replaced with flash content. For best performance it is advised to remove this and put the script tag inside the head of your templates.
The chosen options for "render macro content in editor" don't seem to be respected by the package creator,so it is advised to disable rendering in editor manually for this macro.