When I'm watching a movie and I press the "play" button, iTunes 10 launches. How can I keep this from happening?
Just found this on Lifehacker. I think it's exactly what you're looking for. The post talks about a patch called MMFix, which changes the media control daemon to stop exactly this from happening. Apparently, it comes with a one-click installer.
And, if some reason you would like to remove the patch, just run the one-click installer again and the original rcd daemon will be restored.
(Works on OS X 10.7 Lion, too!)
MMFix hasn't been updated for Mountain Lion yet, but I did find this solution to work, run
in the Terminal.