Drives me nuts that Netflix won't allow this.
I pay all month long, but the only time I could really use it is in the air.
I really do value the fact that Amazon allows this.
iTunes works also, but as mentioned, it's pay per show, and occasionally I've had problems getting things to play in the air. I think that's happened more on my Mac than my iPad, but it does still seem like iTunes wants to check in with homebase even for downloaded videos.
Does anyone know what the whole rule is with iTunes?