Amazon released a new free app today, Amazon Instant Video, that gives U.S. iPad users access to Amazon's catalog of over 120,000 videos. It's great to see yet another rich source for movies coming to the iPad. If you're an Amazon Prime member ($79/year), you have access to thousands of free videos — a subset of their catalog, just as with Netflix. Of course, anyone, whether or not they're a member of Amazon Prime, can also purchase or rent videos (48 hours) for watching on their iPad. In my experience, the cost is similar to the Apple Store, with movie rentals being in the range of $1-4. There's a selection of free movies, and you can purchase movies for as little as $5.
You can either stream the videos instantly via WiFi (hence the app's name), or download them and watch them later when you're offline.
Other features include WhisperSync, which keeps track of where you are in a video, such that when you resume watching it on any device, it continues where you left off. Start watching it on your iPad and later watch the rest of it on your connected TV or desktop computer.
Thre's a small catch, though, with the app. Because Apple wants a 30% cut of everything, including in-app purchases, Amazon, like other vendors, is reluctant to give up that money. So you can't actually buy or rent videos, or subscribe to Amazon Prime, from within the app. You'll have to do that on your desktop computer. But then the content will be available to you on your iPad.
There's currently no AirPlay support, though you can likely enable that via the task manager on your iPad.
You can read more on Macworld.