Ah yes, ‘Homer the Great’. One of my favorite lines is near the end of that episode.
“I now call to order the first meeting of the ancient and mystical order of…No-Homers.”
Fantastic episode.
My favorite for years has been "King-Sized Homer". I think like the “Bart Sells His Soul” eppy, it does deal with a serious topic - obesity and the health problems that can arise from it. I know Homer did it to himself purposely but the underlying theme about obesity’s effects on a person is a serious topic.
So:
Homer can’t stand the thought of participating in Burnsie’s mandatory morning calisthenics, so he concocts a crackpot plan to gain 61 pounds so he’ll be heavy enough to go on disability and work from home.
He confides in Bart about his plan and Bart, of course, wants to do all he can to help:
**Bart: If you gain 61 pounds they’ll let you work at home?
Homer: Y’uh huh, that’s the deal. No more exercise program, no more traffic, no more blood drives or charity walks.
A very, very close second - a tie, really - for me is The Shinning. I love all the Simpsons Halloween eppies, but my favorite is Treehouse of Horror V. Good times!
Bart: Dad, I know we don’t do a lot together but helping you gain 61 pounds is something I want to be a part of. **
Naturally, Lisa objects strenuously:
**Lisa: Obesity is really unhealthy; any doctor will tell you that.
Homer: Oh yeah? Well we’ll just see about that little miss smart guy!
Cut to Dr. Hibbert’s office, where Homer wants advice on how to gain the weight.
Hibbert: (gasps) My God, that’s monstrous. I’ve never heard of anything so negligent – I’ll have no part of it!
Homer: Can you recommend a doctor who will?
Hibbert: Yes!**
The supermarket sequence where Homer is filling up his cart with all the unhealthy crap he can find to eat so he can gain the weight always sets me off on this crazy laughing jag.
And at the end, when Homer seals off the release of the toxic gas by falling into the hole:
**Lisa: I think it’s ironic that Dad saved the day, while a slimmer man would’ve fallen to his death.
Bart: And I think it’s ironic that, for once, Dad’s butt prevented the release of toxic gas.
Marge: Bart! ** 
A very, very close second - a tie, really - for me is Treehouse of Horror V. “The Shinning” is my favorite mini-ep in that show. My favorite exchange:
**
Mr. Burns: Yes, by cutting off cable TV and the beer supply, I can ensure an honest winter’s work out of those low-lives.
Smithers: Sir, did you ever stop to think that maybe it was doing this that caused the previous caretakers to go insane and murder their families?
Mr. Burns: Hmm, perhaps. Tell you what. We come back and everyone’s slaughtered, I owe you a Coke. **
Most of my favorites have mentioned, but I’m surprised no one has mentioned the bowling episode or Who Shot Mr. Burns.
Bowling ep: Burns hallucinates and sees Homer as Pop-n-fresh. The computer matching algorithm to identify Homer later. Skinner recounts how an ‘Up with Miniskirts’ T-shirt allowed Charlie to get the drop on him in 'Nam. School uniform fashion show. “Oops, lost a nail… Well, that’s leprosy for you.”
Who Shot Mr. Burns: I love the sequence of requisitions after the school gets rich-
Willy: “I’ve always wanted a crystal slop bucket” [APPROVED]
Doris: “The cafeteria staff are complaining about rats… I want to hire a new staff!” [APPROVED]
Otto: “You know those guitars that are, like, double guitars?” [APPROVED]
Ralph: “Chocolate microscopes” [APPROVED]
Skinner: “More rubber stamps!” [APPROVED]
22 Short Films About Springfield has been my favorite episode since it aired.
I initially came into this thread to post Homer Phobia. I remember laughing 'til it hurt when me and my friends watched this one back in college.
Marge: I’m very sorry you feel that way, because John invited us all out
for a drive today, and we’re going.
Homer: Woah-ho-ho, not me! And not because John’s gay, but because he’s a
sneak. He should at least have the good taste to mince around and
let everyone know that he’s… that way.
Marge: What on Earth are you talking about?
Homer: You know me, Marge. I like my beer cold, my TV loud and my
homosexuals fa-laming.
Words to live by…
But then someone referenced what is truly and inarguably my favorite episode of all time. Homer At The Bat is a landmark of comedy and probably the only occasion where celebrity guest stars weren’t a disaster in any show.
I mean, come on…
Umpire: Okay, let’s go over the ground rules.
You can’t leave first until you chug a beer.
Any man scoring has to chug a beer.
You have to chug a beer at the top of all odd-numbered innings.
Oh, and the fourth inning is the beer inning.
Chief Wiggum: [in baseball uniform] Hey, we know how to play softball.
…and…
Burns: Smithers, I’ve been thinking. Is it wrong to cheat to win
a million-dollar bet?
Smithers: Yes, sir.
Burns: Let me rephrase that. Is it wrong if <I> cheat to win a
million-dollar bet?
Smithers: No, sir. Who would you like killed?
…and of course…
Barney: And I say, England’s greatest Prime Minister was Lord Palmerston!
Wade Boggs: Pitt the Elder!!
Barney: Lord Palmerston!!!
Wade Boggs: Pitt the Elder!!! [pokes Barney]
Barney: Okay, you asked for it, bud! [punches him out]
Moe: Yeah, that’s showing him, Barney! [scoffing] Pitt the Elder…
Barney: Lord Palmerston!!! [punches Moe]
…naturally…
Marge videotapes Homer on the bench, but when Homer reaches down to scratch
himself in that place baseball players (and Roseanne Arnold) always
scratch themselves, Marge quickly turns the camera away. Children, tell me when your father stops scratching himself.'' Time passes. Kids?‘’
Bart replies, ``We’ll tell you, Mom.‘’
…but most of all, you cannot underestimate the wonder and joy that grips me when the song is played over the closing credits. Often I find myself whistling the tune to myself all these years later.
Greatest. Episode. EVAR!
See, I have a problem with this one. Let’s say I budget a half hour for a run at the gym. Once I cross the 30-minute threshold I’m giving more than 100%. Just yesterday I gave 200%. 
Favorite Episode: In Marge We Trust. It’s got the Listen Lady (Moe: “Yeah well, listen lady …”), die-diddly oodles of Flanders, and best of all, Mister Sparkle!
Akira: [on phone] Hai … Hai … Hai … Bye. [hangs up and turns to Homer, Bart, Lisa] Hi.
Akira: Yes, you have very lucky dishes, Mr. Simpson. This soap is from the sacred forests of Hokkaido, renowned for its countless soap factories.
So many awesome episodes, personally I think Cape Feare is may favorite although I also hold a special place in my heart for some of the Treehouse of Horrors - including the evil Krusty dall and when Homer sells his soul for a donut.
My hubby has one favorite so I am going to cheat and use his - Homie The Clown
I nominate Bart the Daredevil purely for what is the greatest sight gag in TV history
I can’t believe the lemon tree episode hasn’t been mentioned yet.
I cannot Youtube at work, what scene is it?
I am glad someone else likes this classic the best. 
Jim
Homer accidentally skating off the ramp into Springfield Gorge followed by his bloody tumble off the rocks. Of course, the ambulance crashes and sends him over the edge a second time.
I might have to say the one where Homer almost has an affair with the new plant employee, if only because I use the phrase “Can’t talk! Eating!” a few times a week at least.
There was one Treehouse of Horror where Willy filled in for Freddy Krueger.
Lisa: “Imagine going to sleep and not knowing if you’re going to wake up dead?!?”
Grandpa: “Welcome to my world!”
But the king of all episodes is “King-Sized Homer”. My wife never got over the line, “I warsh mahself with a rag on a stee-ick!”, while my favorite is, “I just can’t believe that for once Dad’s butt prevented the release of toxic gas!”
I’d have to think long and hard to answer this question, but I just have to point out an error in the YouTube comments on that clip (not that YouTube users are the smartest people in the world or anything)- there is no such thing as an “uncut” version of Homer’s fall down Springfield Gorge. The version that appears here- with bandaged Homer falling down the gorge- was animated specifically for the episode “So It’s Come To This- A Simpsons Clip Show.” The original as seen in “Bart the Daredevil” does only implies Homer’s second fall.
King-Sized Homer contains my favorite sight gag, like, ever – Homer in the ice cream truck, driving past the school bus, stuffing his face with ice cream. That makes me cry laughing everysingletime.
But my favorite episode of all time? I third (fourth?) this one:
There’s also something so sweet and full of wonder (childlike, but in the best possible way) about Homer in this episode – I don’t think I’ve ever liked him more than the way he is here.
This is just topped by the way Homer says “Ooh, that’s raspberry!” to himself.
Treehouse of Horror VI. I gotta go with that one.
Ad slogans turning into monsters:
“Ah, they’re not so tough.”
“Chief, that was the captain of the high school basketball team.”
“Well, he was turning into a monster, though.”
Kang and Kodos at the end: “Remember the story - we’re newlyweds on our way to Earth Capital.”
Willy as Freddy Krueger:
Skinner: “Children, I couldn’t help monitoring your conversation. There’s no mystery about Willy. Why, he…simply disappeared! Now, let’s have no more curiosity about this bizarre cover-up.”
<Martin’s dream> “Mort - yewww die!”
Lisa: “Mom! Martin died at school today!”
Marge: “Well, I don’t see what that has to do with Groundskeeper Willy.”
Bart: “Uhh…we didn’t mention Groundskeeper Willy, Mom.”
Wiggum: “What are you going to use? Skeleton power?”
And then the classic “Homer in 3D land”:
Homer: “This place looks expensive. I feel like I’m wasting a fortune just standing here.” ::scratches butt::
Frink: “Well, it should be obvious to even the most dim-witted individual who holds an advanced degree in hyperbolic topology, [sub]n’goo-hee[/sub], that Homer Simpson has stumbled into…the third dimension.”
(Then he draws the diagram from Little Girl Lost…)
…“This forms a three-dimensional object known as a “cube”, or a “Frinkahedron” - in honor of its discoverer, n’goo-hey, n’goo-hey.”
And the great ending:
Homer: “Crap! Crap! Crap! Crap! Crap! Crap! Crap! Crap! Crap! Crap!”
Homer: “Ooh! Erotic cakes!”
I would have a hard time naming just ONE favorite. Fortunately, many that I might name have already been mentioned. EXCEPT, for a masterpiece known as…
Marge vs. the Monorail
-The monorail song (“The ring came off my pudding can”)
-“Do you want to change your name to Homer Junior? The kids could call you HoJu!”
-“Batman’s a scientist!”
-The brilliant guest appearance from Leonard Nimoy
-“You don’t scare me. That could be anyone’s ass!”
-``And that was the only folly the people of Springfield ever embarked upon. Except for the popsicle stick skyscraper. And the 50-foot magnifying glass. And that escalator to nowhere.’’
Which contains the Simpsons’ Nerdiest Gag Ever: 1782[sup]12[/sup] + 1841[sup]12[/sup] = 1922[sup]12[/sup]
“The Cartridge Family” known to me as “The Gun Episode.”
For:
- The Gun Shop “Blood Bath and Beyond” (don’t think this shows up when the show is re-run).
- The Blackboard gag – EVERYONE IS TIRED OF THAT RICHARD GERE STORY
- CLERK: “There’s a waiting period for handguns.” HOMER: “But, I’m angry now!”
- HOMER: “But Marge, I swear I never meant for you to (small pause) find out”
Great episode.
Whichever one features “The PTA has disbanded!” and the guy crashing out the window. Funniest moment ever.