I really hate to tell you this, but they cancelled Samurai Jack because the actor that voiced Aku, Mako, died in 2006. Avatar: The Last Airbender actually dedicated the episode Tales of Ba Sing Se to him.
As for a show I would like rebooted, I would have to say, in a sense ironically, ReBoot. It was my favorite cartoon growing up. And being one of the earliest CGI cartoons I can think of, taking place inside a computer no less, it was one of the more creative shows of the time, with many video game references, and technological jargon.