Price, which iPods they work on and how long you get to keep it.
Purchased movies start at $9.99 and are yours to keep forever. They can be viewed on authorized computers, Apple TVs, 5th gen iPods, Classics, 3rd gen Nanos and iPhones.
Rented movies start at $2.99 (except for the movie of the week which is .99). Once you download one, you have +30 days+ to start watching the movie. Once you start watching the movie, you have +24 (48 in the U.K) hours+ to finish watching. Once the movie expires, it's automatically deleted from your hard drive. Rental movies cannot be transferred to 5th gen iPods.
Also, if you have an Apple TV, you can rent HD movies from the Apple TV. Purchased movies are not available in HD.
Some movies are offered for sale, some for rental and some for both.
Best of luck.
