After Otto leaves Becky at the altar, Homer warns her to take off her wedding dress lest she look crazy. This is a possible reference to Ms. Havisham, the Charles Dickens character.
One of the kids in the classroom says D'oh when he drops his camera.
Dr. Zweig (the therapist who helped Marge with her emotional problems) from "Fear of Flying" and Dr. Foster (the therapist who helped Ned with his anger problems from his past) from "Hurricane Neddy" both appear at Marge's insanity hearing.
This is the second time (first time being in "Mayored to the Mob") in which Homer knocks Marge unconscious.
The bar Juggernauts, which was mentioned earlier in "Pygmoelian", is mentioned by Kent Brockman in this episode and is seen briefly.