Sketchcast allows you to draw or type while you record yourself. This example is a student recording their Veteran's Day Poem while they draw.
Another idea could be to draw and explain a concept you have been taught such as a cross section of ground water, a math problem, a diagram, or images for vocabulary words.
Russell Stannard of Teachertrainingvideos.com has a series of tutorials that show how to use Sketchcast. One idea I really like is the idea of channels. And as Russell explains, if you have a classroom account, students can post their Sketchcast and the teacher can subscribe to the channel to see each of the students' Sketchcasts.