http://www.darkhorse.com/Books/18-604/Avatar-The-Last-Airbender-Volume-1-The-Promise-Part-1-TPB
Apparently there is a comic continuation of Avatar:TLA that I assume is going to lead into Avatar: Legend of Korra. Part 1 came out a month or two ago but I just read it.
*Semi-Spoilers/Comments*
The romance component made me want to throw up in my mouth a little bit. The Zuko having a hard time as Firelord reminds me something GRRM said in an interview once. Basically he thought it was wrong for so many fantasy stories to assume that the good guys/main characters will automatically make good kings. Like at the end of LOTR you are supposed to assume that once Aragorn becomes the king everything will be peachy because Aragorn is a cool guy but in truth he may not know jack s*** about being a king. Zuko is what, like 17(?) at the end of the series and he was literally raised by a tyrant. Makes sense that he is indecisive/doesn't really know what he's doing.
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-Merc