Thirty Minutes Over Tokyo - S10-E23
Trivia: During the flight to Japan, Marge reminds Homer that he had seen the Japanese movie "Rashomon" and had liked it, to which he responds something like "I don't remember it like that". This is a reference to that very movie, in which a number of people witnessed a murder and each gave a very different version of the events after what each "remembered".
El Viaje Misterioso de Nuestro Homer (a.k.a. The Mysterious Voyage of Our Homer) - S8-E9
Trivia: When Homer starts tripping on the chili pepper, he sees a distorted vision of Ms. Crabapple and she makes "wah-wah-wah" noises when she talks. These are the same noises teachers are always making in Charlie Brown cartoons.
The Ziff Who Came to Dinner - S15-E14
Trivia: I don't remember all the films presented at the cinema, but there was Eating Nemo, The Fashion of the Christ and A Matrix Christmas. At the opening credits of Cosmic Wars, it's written FOX, a division of Orange Julius.
Treehouse of Horror XIII - S14-E1
Trivia: One of the Homer clones in "Send in the Clones" is the Homer from the early Tracey Ullman shorts.
Trivia: The couch gag in this episode shows the family in the style that Matt Groening drew them on the Simpsons on the Tracy Ullman Show.
Lisa on Ice - S6-E8
Trivia: After Skinner tells the students to report to the "Butthead Auditorium", he says to himself that they "shouldn't have let the students name that." This is a reference to a School from Maryland about 10 years ago that let the students rename their school. Their top pick, "Springfield Elementary", was rejected because of the negative influence of Bart and the show itself.
The Computer Wore Menace Shoes - S12-E6
Trivia: In this episode, Homer has made a very popular website. You can actually visit the site at this URL: http://www.thesimpsons.com/mrx/.
$pringfield (or How I Learned to Stop Worrying and Love Legalized Gambling) - S5-E10
Trivia: Towards the end, Mr. Burns starts becoming insane, growing long hair and long, claw-like fingernails and toenails, and becoming obsessed with germs. This just what happened to Howard Hughes, the eccentric billionaire who died in 1976. Burns also has a plane called the "Spruce Moose." Hughes' plane was the "Spruce Goose," currently displayed in Long Beach, California.
Trivia: When Homer sees the Frying Dutchman ad, he blisses and lean backwards. This is exactly the same shot from "Bart's Friend Falls in Love", when Homer is watching a program about chocolate on TV, only the frame is flipped. (00:04:30)
C.E. D'oh! - S14-E15
Trivia: At the end of this episode, Homer has a barbecue with a banner that reads "Homer's 305th 'Everything is Back To Normal' Barbecue", even though this is the 306th episode. This is because everything was not back to normal at the end of Who Shot Mr Burns? Part 1, the only Simpsons cliffhanger.
Tree House of Horror VI - S7-E6
Trivia: In the segment Homer3, you can see at one point in the background of the 3-D world a tea kettle. This is a reference by the animators to the first object ever digitally animated into 3-D, a kettle. You can also see the number 733, which if you look on a normal phone it spells out PDF, the software they used to make the sequence. There's a special on these on the 7th season DVD's.
Trivia: The poem that Homer attempts to read is the weird poem that Steve Martin recites in both "The Man with Two Brains" (1983) and "L.A. Story" (1991) ("Oh pointy birds, oh pointy pointy...").
Trivia: In the first shot inside the bomb shelter after the whole town has crammed in, you can see Waldo from the "Where's Waldo?" books at the top of the screen.
A Tale of Two Springfields - S12-E2
Trivia: Springfield is split into two area codes, 636 and 939. This would put half of Springfield in Missouri and the other half in Puerto Rico.
Homer's Barbershop Quartet - S5-E1
Trivia: The reason the name 'The B Sharps' is so funny (at least to a musician) is that in music there is a natural half step from B to C. This makes a B sharp the same as a C natural. It is almost never referred to as "B sharp", but instead as simply "C".
Tree House of Horror XI - S12-E1
Trivia: There is a scene from Kent Brockman's report on the dolphins that was cut out in syndication. After the dolphins warn him not to mention their attacks, he "corrects" himself with him saying "Killer Dolphins" and says "Killer Italians" (and features a photo of Luigi the chef).
The Simpsons Halloween Special: Tree House of Horror - S2-E3
Trivia: During the opening graveyard scene, notice the gravestone which says Paul McCartney. Creator Matt Groening is a big fan of the Beatles, and during the 1960's, a conspiracy theory was being spread that Paul McCartney had been killed in a car crash and was replaced by a lookalike.
Trivia: The comic book seller bans Bart and Milhouse for life. When he places their picture on the wall, there are other persons banned. The other persons are: Sideshow Bob, Nelson, and Matt Groening, the creator of the Simpsons.
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer