I'm sure most traditional animators already knew this, but there has been this program around for years that has become free because the developers consider it old and ugly. However it seems pretty cool to me, admittedly I'm not a traditional animator and I've only played with it for about an hour.
I know my example animation is rather shit, I just want to put something up on the blog that looked like F.B.F animation. I think this is a really nice little app to work with and you can even bring in sound files if you need to animate to audio. The developer was trying to crowd fund an upgraded version called Animation Paper but unfortunately they didn't hit their target so I don't know if that'll ever happen. But till then we have this, for free.