Nickelodeon.
Yeah, Avatar is produced in the US and Canada (most Nick shows are strongly tied to Canada, if not primarily made there). Some will argue that it's still classified as "Anime" because it's animated by a Korean animation studio. Of course, the blinding hole in this is that, in Western culture, Anime refers to Japanese cartoons exclusively, not just "Asian" in general. The other, more important point of this though is that about 90% of cartoons EVERYWHERE are animated in Korean animation studios. They're ridiculously cheap compared to other studios, and as the primary cost of producing a cartoon is the animation (unless we're talking about shows that are primarily CGI), most producers contract with Korean groups for the majority of their animation.
Flash Leopold, UK Superhero, you know where I'm going with this by now...