You haven't learned to love "Super Why!"? The spelling princess is my favorite; I was state high school spelling champion of Virginia in 1984 ;-).
Have you tried the David Attenborough nature documentaries, such as "Planet Earth" and "Blue Planet." (There are many others, many available streaming on Netflix.) Our little boys (3, 6, 8, 10) love them, and recite nature facts endlessly, and David's soporific yet nerdy voice makes the baby fall asleep, too!
My oldest just turned 5, so he’s barely starting to watch stuff like Mytbbusters and nature shows. He doesn’t really “watch” tv so much as he has it on while he plays with something else, anyway. I grew up watching all the science shows, but now I don’t have much patience with them since the internet is so much better and faster.