Nickelodeon have announced Avatar: The Legend of Korra, a new animated 12-episode mini-series which will serve as a sequel to Avatar: The Last Airbender. The name seems to be inspired by the name that the previous series went under in the UK and other countries, The Legend of Aang.
The new series will be set in a different time period to the original series and focuses on the emergence of a new avatar (someone who can use all four of the elemental forms of magic), a girl named Korra. The single screenshot revealed hints at a slightly more technologically-advanced time period, with much taller buildings than in the original series, although the traditional Asian influence remains strong. The accompanying press-speak suggests that the series will build on the mythology of the original series with a hotheaded female lead. The series will debut in 2011.
To reiterate, this is a sequel to the excellent, possibly classic, animated series, not the M. Night Shyamalan movie.
More detailed information has emerged. The Legend of Korra is set seventy years after the conclusion of Avatar: The Last Airbender. Korra, a member of the Southern Water Tribe, is already the Avatar when the series starts and has mastered three of the four elements, leaving only airbending unmastered. She is looking for Tenzin, the son of Aang (and presumably Katara), who will teach this skill to her. A principle location will be Republic City, a metropolis powered by steampunk technology which is riddled with crime and where the people, a mix from all four nations, are becoming disenchanted with magic-users in general.
This sounds more hopeful. A rebellion of the 'normal' people against all of the magic-users and more focus on one location sounds like good moves, throwing up good storyline possibilities.