When the episode "You Got Fucked in the Ass" (aka: "You Got Served") first aired, the leader of the Orange County boys had a hat which read "Lil' Shiit." This was edited to be "Lil' Sheep" before the second airing of the episode that exact same night.
At Chef's house, there is a portrait of Isaac Hayes, who does the voice of Chef. This was a color-modified version of the CD cover of Hayes' 1995 single "Fragile".
First appearance of Butters' "I've Got Some Apples" song.
The address of the dance studio that Chef is training Stan's crew in is 1138, most likely a nod to the common numbers that appear thru Star Wars and many of George Lucas' works.