In the newspaper headlines, "Receives" is spelled wrong.
"Jesse Jackson, is not the emperor, of black people!" - A variation on the often-heard retort by callers to a talk show - Jesse Jackson, Al Sharpton, et al, do not speak for the entire black community.
Jesse Jackson created the Rainbow Coalition in the 1980s. In his office is a wall hanging touting the RainbowPush Coalition.
"little person" - used as a euphemism for dwarfs and midgets, along with "short person" and "vertically-challenged person" (something which can be said of a giant too, but it's not nearly as offensive applied to them)
In "Cartman joins NAMBLA" Cartman says that midgets piss him off. In this episode, he's clearly more amused with them. It turns out that Mr. Nelson is a dwarf, not a midget, so you can say that midgets piss Cartman off, but dwarfs crack him up. A midget is a short person who looks like a miniature of a normal person or a figurine, while a dwarf has deformities that make him look like a doll.
In the principal's office behind Mr. Nelson, on one of the shelves in the bookcase, is a picture of Principal Victoria and Rosie O'Donnell.
Randy at the Laugh Factory rips on Michael Richards, who got infamous there when he responded to a heckler by using the N word repeatedly, to the point where the heckler and his friends left the club and later sued him. Gloria Allred came to represent them, and Michael Richards appeared on TV several times to apologize for his behavior that night. A caricature of Michael Richards appears later in the episode to defend Randy against the rednecks.
The sidewalk in from of South Park Elementary now has a curb and a gutter. The school flag now has some greenery growing up around it.
Principal Victoria now has a secretary, Stacey. No idea what she looks like yet.
A Hunter S. Thompson poster sits behind the drummer at Viggo's.
Randy asking the Senate to ban the N word refers to the symbolic ban the New York City Council paased on February 28, 2007 against the N word.
"Caroline! don't go into the light!" - Tangina's line from Poltergeist (1982).
The song used during the Cartman-Nelson fight and in the ED is "Down With The Sickness" by Disturbed.
Cartman said he watched the Wheel of Fortune clip on YouTube about 60 times, but when you actually look for the SP clip, you get this:
On the other hand, the Kramer Rap and the tirade it was made from are both still visible and apparently not in violation of TOS.
"Look, look how his face gets all red! He's like a little strawberry!" - as far as I can tell, it didn't change colors at all. This has been fixed in subsequent airings - Mr. Nelson's face does turn red.
Mr. Nelson tells the kids to say "hello, fatso!" Instead they say "Good morning, fatso!" in a cheerful manner. This too was fixed in subsequent airings: "Hello, fatso" in a listless manner.