This next item was originally reviewed over at The Land of Whatever around the time of the feature film remake, but DePatie-Freleng had the first crack at Dr. Seuss' The Lorax, which premiered on CBS in 1972, a year after the book was released.
It was Seuss' commentary on ecology, among other things. Eddie Albert (ex-Green Acres) narrates, but otherwise, the majority of the voices were performed by Bob Holt. Some of the work was edited and reused for a TNT special, In Search of Dr. Seuss, more than 20 years later.
Right now, in honor of Read Across America day, which took place today, here's The Lorax.