Avatar the Last Airbender is a Nickelodeon animated series that concluded its third and last season last year I believe. This is one of the better animations that has aired/been developed by Americans (I assume it was developed by Americans). It is a welcome change of pace from shitty animations that one used to and may still see on Cartoon Network. The series is about people who can manipulate one of four elements (water, air, fire, earth) called benders and the avatar who can bend all four. The world is divided into four nations with each nation specializing in one of the elements and the all-powerful avatar keeps the balance between the nations.
The main character is about 11 or 12 years old and he and his nation are based on Tibetan monks. I think this is one of the best cartoons ever made (all though I think the show seems to lose some of its magic in the third season as it appears to become more serious and drop a lot of its humor and freshness). There's a bit TOO much China-bashing in the show with China's first emperor being a short idiot who dies an ignominious death. Other than that, it's quality.
A sequel to the show is currently being aired in its first season called The Legend of Korra. It takes place about 100 years after the first series and there's a new avatar who is female and older than the avatar in the first series. This animation has great drawn and computer-rendered animation, but the magic is gone. All the freshness of the first series is gone and this show lives in its shadow much like episodes 1 and 2 of the Star Wars prequels lived in the shadow of the first trilogy. It's decent enough to watch, especially if you liked the original.