With Amazon Instant Video, you can:
• Stream thousands of titles available from Prime Instant Video at no additional cost with a Prime membership, or watch over 120,000 videos available from the Amazon Instant Video store
• Download purchased and rented videos from Your Video Library
• Shop over 120,000 videos available from the Amazon Instant Video store by visiting Amazon
• Add videos to your Watchlist from a PC, Mac, or Kindle Fire for later viewing on your iPad
• Subscribe to a TV Season Pass by visiting Amazon and episodes will automatically be available on your iPad the day after they air
• Start watching on your iPad, and resume watching right where you left off on a Kindle Fire, PS3, PC, Mac, or hundreds of models of connected TVs and Blu-ray players with Amazon Whispersync.
You need to have an Amazon Prime account, which is $79 a year with a one month free trial. The Amazon Prime program, also gives you free shipping and many other things. Available for iPad only at this moment, on the App Store [Link].