we noticed that Nick's Avatar: The Last Airbender (which
I had never heard of) has been added to the iTunes Music Store [iTunes link].
Nineteen episodes from season 1 are available for $1.99US each.
Season 2 follows the same subscription model that Apple is using to distribute The Daily Show and The Colbert Report: For $29.99US, you can purchase a season pass to Avatar and receive each episode automatically as they're added to the iTMS. Before you do the math, note that season 1 is listed as a "partial season," so it isn't certain how many season 2 episodes you'll get for your thirty bucks.