Making videos on the iPad
White Board Type Apps
There are several whiteboard type apps that allow you to make Khan Academy style videos on the iPad. Some examples of these are shown below. The first two ShowMe and Educreations were some of the first available and in addition to being able to record and save screencast videos they also offer libraries of videos that have been shared by other teachers.
Explain Everything was released in 2011 and has become a very mature creation platform with its hallmark being the ability to save videos to a number of formats and locations including YouTube.