Here are two free plug ins by Glitchmachines that are worth exploring. Remember that when you install a new plug in you will need to activate it within Adobe Audition and likely any other audio or video programs where you intend to use it.
Are you interested in trying out other sound production tools, but cant afford Protools, Digital Performer, or Ableton Live?
This is a great tool for $60
Here are some interesting visual tools to create textures, tones, beats, etc either in your browser or via small applications you can use on your computer.