Storyboard That is a robust web tool that allows students to create and edit Storyboards. This site is simple to use and allows users to drag and drop stick figures and screen elements, as well as add their own content, to the storyboard time line. Enough tools and features to be really useful and not too many to confuse young users, this is a nice way for students to create storyboards for class projects, videos, or anything else you can think of including comic strips. There is a nice educator portal which has some lesson plans and example student work.
Not free, but free trial and reasonably priced for teachers
"Bring the world's best storyboard creator into your classroom!
From first grade to graduation, Storyboard That engages students with digital storytelling in the classroom."
This site has a 30 second blurb on many topics that we teach from the money supply to Henri Matisse from the space station to the properties of chemicals.
Qwiki allows users to learn more about a variety of topics through multimedia and storytelling. Users can also contribute content to make Qwiki even better.
Qwiki instantly makes a 1 minute educational movie on any topic. A must try resource! Works by typing in a search term. Great for visual/auditory learners... and teachers. http://ictmagic.wikispaces.com/ICT+&+Web+Tools