Are you a Amazon Instant video user? Well if you are there is an update coming to the app which allows you to download movies or TV shows to your device, so you can watch them off line later.
You can only download over a WiFi network not cellular, and it appears at the moment that not all the Prime Instant video content is downloadable, but this is a massive change to the service and I for one am going to use it to its full potential.. 😉