Playing with my iPad yesterday and I found this app/internet service, verso, for classroom flipping. I'm absolutely in love with it. It is very inexpensive too. They give you three classroom flips for free and then after that they are less than a dollar each which I think is very affordable. I might try this with my senior physics class this year. They even have a library of resources to use that contains some great links. Check out the video to show students how it works on the lower right hand corner of their home page. It is very well done.