Storyboard That - Storyboard That is the world's best online storyboard creator.
StoryMill - Developers and publishers of Mac, Win, and iOS productivity, home and office and writing software such as MacGourmet, Paperless and many more. Based in MN.
Storybird - Visual storytelling community
BlankPage - Stay motivated to write, and finish your story
Storyboarder - Storyboarder makes it easy to visualize a story as fast you can draw stick figures.
Manuskript - Open-source tool for writers.