Pinnacle Studio for iPad is a powerful video editing application. Pinnacle Studio allows you to edit, crop, add text, audio, still images to video files on your iPad. In my opinion this is the very best video editing application available for the iPad.
Pinnacle Studio is $9.99 in the App Store: Pinnacle Studio Pro - professional video editing - Corel Inc. (iPad)
Pinnacle Studio is also available for the iPhone: Pinnacle Studio Pro - professional video editing - Corel Inc. (iPhone)
This is an updated preview of the app, I previously did a preview back in 2012: http://www.crizzo.net/2012/10/pinnacle-studio-for-ipad.html.