GoAnimate is a fun site that allows you to create animated videos like this one:
SH Summer Tech Challenge by Mickie Mueller on GoAnimate
I think students would love making animated videos. Like so many of the tools in the Summer Tech Challenge, GoAnimate could be another way students could show what they have learned. For example, in history class, have students make a modern day version of George Washington crossing the Delaware. Or in a literature class, have students reenact a scene from Romeo and Juliet only setting it in modern times. Both of these examples would definitely give you an idea whether or not your students understood what was happening in each of those situations.
You could also use GoAnimate to introduce a unit of study. You could put together a video and share it with students prior to starting the unit.
Math teachers could have students create videos for factoring or explaining a proof or pointing out the geometric shapes that they see on a daily basis. GoAnimate could be used in just about every subject area.
Be sure to check out the GoAnimate Lesson Gallery for other ideas!