Avatar: The Last Airbender has Prince Zuko. Though he may not have been intended as such at first, the creators quickly caught on and lampshaded the hell out of his Mr. Fanservice status in the second and third seasons.
The Legend of Korra has Mako, who, unlike Zuko, seems completely intended to be one from the beginning, as he's actually had more outfit changes than Korra and his scenes normally include a lot of unnecessary panning and posturing. Even the creators, his bio on the Nickelodeon website and his voice actor make it a point to mention that Mako is good-looking.
In The Secret Saturdays, Doyle Blackwell is Zak's Cool Uncle who is a mysterious but loving badboy with sarcasm and a jetpack. He is also the only male in existence who can pull of a ginger mullet-mohawk combo.