Coach's Eye is a video analysis tool that allows you to shoot video on an iPhone and the review it in slow motion or frame by frame. You can also annotate video with drawings or audio commentary. The quality and control of the slow motion is superb.
Although designed for sports use, I am sure users will find it useful for many other kinds of video. This great example was shot earlier by my friend Kevin McLaughlin @kvnmcl http://www.youtube.com/watch?v=y1fl4e2j2Wo&feature=youtu.be
Currently available for £0.69 / 0.99$