Definitely Homer vs. the 18th Amendment.
Banner: Are you the Beer Baron?
CBG: Yes, but only by night. By day, I’m a mild-mannered reporter for a major metropolitan newspaper.
Banner: Don’t crack wise with me, tubby!
CBG: Tubby?! <looks down> Oh yes, I see…
Homer: Going out. Not back avenge deaths.
Homer: To alcohol- the cause of, and solution to all life’s problems.
It’s because of people like you that this show won’t die a merciful death.
Not with that attitude.
This one includes a couple of my favorite quotes within seconds of each other. “Lousy Smarch weather!” and then upon seeing a sign on the thermostat that says “Do Not Touch. - Willy”, Homer replies “Do not touch Willy. Hm…Good advice” and cranks the heat up.
…and falling through an open manhole cover into the sewers. “And that’s when the C.H.U.D.s came at me.”
When I have the occasion to rebut some yahoo’s trashing of NYC as some kind of crime ridden nest of ghetto thieves and self-centered money-grabbers, I bring out Marge’s line: “Of course you’ll have a bad impression of New York if you only focus on the pimps and C.H.U.D.s.”
The first few times I watched that episode, I laughed over missed Marge’s line about the Smarch weather. She says something like “The PTA was meeting to discuss those mistakes on the school calendars.” 
I agree with You Only Move Twice
Hank: Uh, hi, Homer. What can I do for you?
**Homer: ** Sir, I need to know where I can get some business hammocks.
Hank: Hammocks? My goodness, what an idea. Why didn’t I think of that? Hammocks! Homer, there’s four places. There’s the Hammock Hut, that’s on third.
Homer: Uh-huh.
Hank: There’s Hammocks-R-Us, that’s on third too. You got Put-Your-Butt-There?
**Homer: ** Mm-Hmm.
**Hank: ** That’s on third. Swing Low, Sweet Chariot… Matter of fact, they’re all in the same complex; it’s the hammock complex on third.
Homer: Oh, the hammock district.
Hank: That’s right.
I have to go with the Tomacco episode. So many laughs per minute with that one.
Crap. I looked down a little under my post and saw the hallucinogenic pepper one with Johnny Cash as the coyote. I forgot that was my favorite episode! And then also Deep Space Homer and the Halloween episode where Homer makes the time machine.
Damn you thread! How dare you make me cho-cho-choose!!
(From a different conversation)
Hank: You ever see a man say “good-bye” to a shoe?
Homer: Heh heh… twice.
Then there’s Mary Ann’s Hammocks- the best thing about that is Mary Ann gets in the hammock with you! (Not really.)
Yes! A kindred spirit.
“You’ll never grow anything on that old Simpson farm.”
“Oh yeah, why not?”
“You need a ph of 6.7 or so, and yours is up around 9.”
“Oh, that’s just superstition.”
As I view this thread, there are four Google hammock ads on the screen. Truly, we are living in a golden age!
No one has mentioned “Trash of the Titans”? The episode where Homer becomes the sanitation commissioner. With special guest stars Steve Martin and U2.
One of the all time great musical numbers too:
Oh, the garbage man can, Marge. The garbage man can . . .
Who can take your trash out?
Stomp it down for you.
Shake the plastic bag and do the twisty-thingy too?
The garbage man . . . oh, the garbage man can.
The garbage man can and he does it with a smile and never judges you.
Marge: Who can take this diaper?
GM: I don’t mind at all.
Wiggum: Who can clean me up before the big policemans’ ball?
The garbage man . . . yes, the garbage man can.
U2:
The sanitation folks
are jolly, friendly blokes.
Courteous and easygoing!
They mop up when you’re overflowing . . .
and tell you when your arse is showing!
Apu: Who can?
Mel: Who can?
Ned: Who can?
Oscar: Who can?
The garbage man can!
Bart & Lisa: 'Cause he’s Homer Simpson man!
Again, another vote for You Only Move Twice. It’s a wonderful episode and I enjoy it…
From memory: “If you would kill some people on your way out, it’d really help me”
Brendon
Whereas I’d like to understand why the excruciatingly-not-funny Australia episode rates - at least, to anyone who has been here.
I’m sorry, but I think the episode is hilarious. I never saw it as a dig at Australia and Australians, but more at Americans and their geographic ignorance (like the gag where there is a building that says ‘Australia’ by taking ‘Austria’ and correcting it by inserting an ‘al’). And it has my single favorite moment of all time in the Simpsons, Homer crying and singing “God Bless America” as he watches the toilet flush the “correct, American way”.
According to wikipedia, a lot of Hank Scorpio’s dialog was unwritten, simply ad libbed by James Brooks. My favorite part is Scorpio handing the sugar to Homer.
I’m pretty sure he’s singing “My Country 'Tis of Thee” (and I think the ep’s funny, too, though not in my Top 10).
Albert Brooks. Non-actor James L. Brooks is one of the producers/creators of the show.
From the beginning with Martin playing the My Dinner with Andre video game, complete with bon mot, trenchant insight and tell me more buttons, to Homer watching McGarnigle at the end- “IT MEANS HE GETS RESULTS YOU STUPID CHIEF” I gotta say the Junior Campers episode.
(another one.)
Hank (to Homer): Don’t call me Mr Scorpion. It’s Mr Scorpio, but don’t call me that either.