I can't agree enough with Timothy Burke that Avatar is one of the best shows on TV right now. It's a great mix of kid's escapism, combined with realistic drama that takes itself seriously, but doesn't treat itself too seriously, if you catch my drift.
I cannot stress enough that if you like Avatar, you must check out Fullmetal Alchemist. It's hard to convey just how good this show is without sounding like Gene Shalit reviewing Sleeping Beauty, but the last four or five episodes broadcast have convinced me it deserves a place in drama next to Faust and Macbeth.
The subtlety with which the characters are drawn is masterful. In fact, there is no such thing as a minor character in this show-- this show puts Chekov's dictum about drama to shame by making even the anonymous bartender you meet in episode 1 serve at least double duty. The plot-- ye gods, every time you think it can't get any more complicated, it does, but it never feels artificial. All actions are drawn directly from the personality of each character, and I've yet to see a scene that didn't ring true (except for one very wrong explanation of the human body, but that's another story, and may yet be salvageable).
I'm going to have to buy the DVDs and watch each episode at least twice, I think, to grasp all the subtleties, but this is clearly one for the record books.