Everything I needed to know about Gary Stus/Mary Sues, I learned from Garth Marenghi's Darkplace.
Also, I must say, Avatar is one of the very few kids' cartoon shows made in recent years that makes me actually feel GOOD about what our youth are watching. It's well-written with non-annoying characters, consistent animation quality, and a plot that actually moves, which is far, far, FAR more than I can say for most shonen anime these days. Avatar is, quite simply, just BETTER than 90% of similar anime targeted at a similar audience, and I guarantee you it'll rot kids' brains and turn them into annoying manga cows wielding YAOI paddles far, far less quickly than shit like Naruto.
Let's face it, kids, even though it ISN'T anime, Avatar should be posted here as a warning to Japan that they better shape the fuck up at making their own rape cartoons better and more interesting before certain corners of the West start beating them at their own game.