My daughter is the same age. Among kids' shows, she loves Dinosaur Train (which has more educational value than it may first appear, teaching not just paleontology facts but scientific method as well as emotion self-awareness and other things). Mister Rogers is also a favorite, though that show is harder to find.
But her absolute favorite shows are the David Attenborough wildlife series (Life of Birds, Life in the Undergrowth, Life in the Freezer, etc.). The way they are produced makes them even more accessible and appealing to preschoolers than most nature shows. If your child is even remotely interested in animals or nature, give them a look. She also loves ballet movies -- if you have a child who loves fairytales, music, or dance that might be something less obvious to try.
She went through a Sid the Science Kid phase but has outgrown that show, though, unlike other posters, I do think it's pretty good for reaching children at a particular level. Ditto for Caillou. Could never get her interested in Super Why or Word World or any other PBS shows. Not sure why!
Jenny
