Marge mentions that "Frasier" (1993) from Cheers sounds like Sideshow Bob. The actor Kelsey Grammer voices both Frasier and Sideshow Bob so Marge is correct.
There is no point in the United States where five states meet. This is a parody of the Four Corners Monument, which marks the point at which the states of Colorado, Utah, Arizona, and New Mexico meet.
Bart is implied to be a fan of the Harry Potter series when Bob says that it will be the greatest murder since Snape killed Dumbledore to which Bart says that he hasn't gotten to that part yet.
Walt's radio station of choice is 89.4 FM The Spur. This means the station is legally not allowed to air commercials per FCC regulation.