The first episode of the sequel to Avatar the Last Airbender begins airing on April 14th on Nickelodeon, but you can watch the first episode for free on iTunes. It's called The Legend of Korra and takes place 70 years after Last Airbender.
http://itunes.apple.com/us/tv-season/the-legend-of-korra-vol.-1/id511441792 (http://itunes.apple.com/us/tv-season/the-legend-of-korra-vol.-1/id511441792)
Avatar Korra, a headstrong, rebellious, feisty young woman who continually challenges and breaks with tradition, is on her quest to become a fully realized Avatar. In this story, the Avatar struggles to find balance between tradition and modernity, the bending and non-bending world, and within herself.
You can watch the second episode as well on their main site i think.
I love it. Not only is it just as good as the first one, its a natural evolution of the mythos and has found it own path in the avatar series.
I was so worried about it being disappointing either by failing to be its own show or just not having interesting characters.
Two thumbs up!