Storyboarder for Mac, Windows and Linux is awesome, but needs an iPad version and soon
I ran across this free app Storyboarder, which is an impressive storyboarding app that can import a script and you can do the artwork of storyboards with onion skinning and various pens, and it will export to Premiere, Final Cut, AVID, PDF or animated GIF. And it includes a shot generator with 3d figures.
Honestly my only complaint is that it needs an iPad app (which they say they are working on, but are a very small team, so who knows). Using it on the Mac would be better if my WACOM tablets hadn’t been EOLed.