Hi Hi Puffy AmiYumi
Via The New York Times: Hi Hi Puffy Ami Yumi, which debut on November 19th on the Cartoon Network, is an animated series based on two real Japanese pop stars, Ami Onuki and Yumi Yoshimura, a k a Puffy Ami Yumi.
However it is NOT a Japanese import,and it's not anime. Ms. Onuki and Ms. Yoshimura also appear in each episode, doing live-action skits in a mixture of Japanese and accented English, with songs in the original Japanese (without subtitles).
You might already be a little familiar with them cause they sing the Theme song for the Teen Titans show on the Comedy network
You can hear more samples of their music on the Sony Music Japan site or the Sony Japan PuffyAmiYumi site.
Update The Pop Duo in the New York Times Style Section Jan 16 '05