DS loved Peep, Time Warp Trio, Grossology and Magic School Bus at 4. He'll be 6 next week and I was just getting ready to ask this same question! We screen what he's allowed to watch pretty carefully and he does not get to watch TV with commercials hardly ever (thanks to Tivo).
Right now he watches Toot and Puddle, Future is Wild and Phineas and Ferb pretty regularly. We have ordered the entire Super Mario Brothers on DVD from Netflix and he loves it. He also likes ChalkZone and sometimes Zula Patrol. We also watch Amazing Race together and some of Time Warp and Mythbusters depending on the topic.
He also has a deep love for the Food Network Challenge :-)Which I think is entirely my fault!
