The rare surviving test footage of the Pogo animated short entitled "We Have Met The Enemy And He Is Us," from 1971, is up on YouTube.
Walt Kelly, the creator of Pogo, was so unhappy with the Chuck Jones-directed "Pogo Special Birthday Special" cartoon in 1969 that he and his wife set out to do an animated short themselves, with just the two of them working as animators. The work was so hard that it's said to have hastened Kelly's death from complications of diabetes two years later.
It's a nice little environmental-themed cartoon, very much in keeping with the early Earth Day celebrations that inspired it (and that Kelly lent the cartoon's title to promotions for). Plus, in this early stage (most of it is very rough animation, which would have been finished off later) Kelly himself does all the voices.
Part One can be found here:
http://www.youtube.com/watch?v=XUExCF98J80Part Two here:
http://www.youtube.com/watch?v=_508n4y9qa4Thanks to
Daily Cartoonist for the links.