I spent the morning having the Final Draft vs. Screenwriter vs. Montage debate (again!) and finding myself unable to decide which, if any, might be worth the $150+ price tag when I came across a reference to CeltX. It's advertised as an "integrated media pre-production application" which means that it manages all of the organizing, formatting, and collaborating needed to produce a film, documentary, podcast, play, etc.
The reviews are largely positive, and I was pleased to see that a storyboarding feature is included. I'm not sure if it will replace my corkboard/index card/marker system, but with the ability to add images and sound files, it's a tempting option. Plus, it will enable me to work away from home without bringing a deck of scene cards to shuffle around.
The best news came when I found out that CeltX was free. Yup, FREE. It's open source and available for Windows, OS X, and Linux. I've already downloaded a copy and started playing around. So far, I'm encouraged by the interface and ease of use. If nothing else, those considering the mainstream options should give CeltX a look before buying.