Comedy Central, they are still great and haven't left their roots unlike channels like G4 and MTV. My favorite shows on their now are South Park, The Daily Show, The Colbert Report and a few others I can't think of at the moment.
Many people think Cartoon Network has jumped the shark. I don't think it did. I think people just outgrew the channel and/or cartoons. They do have shows I don't like such as My Gym Partner's A Monkey and Squirrel Boy, and they shouldn't be showing live action movies, but I love to watch Adult Swim, Ben 10, Foster's, Storm Hawks and Billy and Mandy. I don't watch Nickelodeon that much anymore however, save for Avatar. I haven't watched the Disney Channel since 1997.