Prezi works with size and an almost unlimited canvas to allow one to create dynamic presentations. It offers students a lot of freedom and the ability to "backwards design" and create a meaningful "big picture" concept.

This student took advantage of Prezi's unlimited canvas. If you watch the entire presentation you'll see the surprise at the end.

There is a free version but for $2.99 you can purchase the Director's Pass, which gives you so many more options. Students can import images (even their own drawings) or use existing ones, create voiceovers and put the entire animation into a film. See the overview linked here.