I set up a quick system to allow ScaleNine themes to be used in Flex without having to download the source files from the homepage. Simply copy one of the following urls and paste it into the source attribute of a mx:Style tag in your working MXML under the Application tag. However, If you decide on using one of the themes I would suggest downloading the source for the theme you settled on and load it into your Flex project. A couple of weird things happen if you don’t do that, like disappearing images.
Obsidian Theme: http://try.scalenine.com/obsidian/obsidian.css
iTunes 7 Theme: http://try.scalenine.com/itunes7/jukebox.css
WMP 11 Theme: http://try.scalenine.com/wmp11/wmp11.css
Moxy CSS Theme: http://try.scalenine.com/moxy/moxy.css
Minty CSS Theme: http://try.scalenine.com/minty/minty.css
Shadow CSS Theme: http://try.scalenine.com/shadow/shadow.css
Darkroom Theme: http://try.scalenine.com/darkroom/darkroom.css
Vista Blue Theme: http://try.scalenine.com/vistaBlue/vistaBlue.css
Note: You must run/compile your project to see the theme get applied. It would be nice to see the theme change a project right inside Flex Builder rather than having to compile/run it. Maybe in a future release.