I'm noticing more and more little references to Jack and the gang in the classic Warner Bros cartoons. Some, like the Benny-esque Casper Caveman in "Daffy and the Dinosaur" (he was voiced by Jack Lescoulie) or the numerous "Jack Bunny" characters, are pretty obvious. Jack is caricatured in "Malibu Beach Party" and one or two other cartoons, and of course he voiced "himself" in "The Mouse that Jack Built."
I think I'll start to put together a list of other references that are directly or indirectly related to Jack and the program--the "auctioneer" voices, the tag line "so round, so firm, so fully packed," and so on. Just noticed another one recently: in the 1948 Bugs Bunny carteoon "Hot Cross Bunny." This is the one in which Bugs is an experimental rabbit and a short, weirdly-accented mad doctor proposes to switch the bunny's brain with a chicken. In the operating theater, Bugs mistakenly thinks he's supposed to perform for an array of stolid, scowling doctors, and he breaks into his routine...to silence, not applause. Bugs cringes a little and mutters, "Gee, what a tough audience! Not like in St. Jo' . . . they loved me dere!"