For a really old one, I remember reading in the book "The Moose that Roared" that the last thing Jay Ward productions did outside of Cap'n Crunch commercials was a series called "Rah Rah Woozy" about a mouse playing college football. Ward was a big fan of College Football, you see. Hence the Wossamotta U Bullwinkle arc. Now other than some thin recap of the premise in said book (I don't feel like digging it out right now), there's little info on it and there's no footage of it anywhere. This was one of the few pilots Ward productions finished, and there are several that just made it to the script/recording stage that also sounded good. Like a Lone Ranger parody where he was old and senile (I think...again, don't wanna dig out the book).
Another old pilot was a Jeffery Scott written, Ruby Spears produced "Captain Carrot and his Amazing Zoo Crew" cartoon series. Now, I really feel that this could have been the same sort of wacky super hero show like the 1979 Plastic Man series that made up for the lack of allowed violence with wackiness, and Captain Carrot really deserves to be something more than a footnote in DC comics. Too bad it never became a cartoon, otherwise the comic would have become mainstream (same way a certain Turtle based comic and big blue insane super hero did). Sure it got that comeback 3 part special comic series years ago. Other than that there's like..some Robot Chicken skit. Only time they were ever animated.