I discovered an online tool for storyboarding called Shotbox. It looks nice, and it might be useful to order and time your individual storyboard panels. Add sound and create an animatic. Export in different ways.

However, you can't draw inside the program. You have to import your drawings, one by one. I really hope they will create a bulk upload button, because it's just too much work to do this per panel. But it's in Beta and already very promising, so check it out!