Adobe Voice. Free iPad app. Easy! You can choose pre-made templates or simply import your own pictures and make your own. Do voice over as pictures advance. They also have a music library with a number of different genres of music clips. Especially nice for those who are camera shy or want to create a story telling video. Another thing I like about it, is that it challenges me to keep things simple, short and to the point. Also makes it easier to do just that.

Intro Designer. Free. An iPhone app (maybe iPad) to make short intro style videos.

Filmic and TouchCast are other apps that I have not used but that have been recommended–especially for creating special effects like retro, b & w, etc.