Thought this is pretty good it uses airplay to stream video between ios devices my first test I've been streaming a few movies between Itunes on my pc to my Ipod it seems to work really well I guess I can take some off now and save a little space. I know airvideo and others exist but I thought I'd mention this one as it's free and doesn't need additional software installed. http://itunes.apple.com/us/app/airview/id412370918?mt=8#
