l Crossroads of Destiny l
Season One just ended. It's supposed to be a mini series, unlike the Last Airbender. The whole series is only supposed to be a little over 20 episodes or so.
Unfortunately, the next season isn't due to air until around April of 2013.
Whole series is planned to be a total of 52 episodes.
Book 1 - 12 episodes
Book 2 - 14
Book 3 - 13
Book 4 - 13
edit: broken quote bracket.