HOMER: Kids, there’s three ways to do things: the right way, the wrong way and the Max Power way!
BART: Isn’t that the wrong way?
HOMER: Yes, but faster!
Moe: Bring us your finest food, stuffed with your second finest.
Waiter: Very good, sir – lobster, stuffed with tacos.
[Afterwards we see the remains of the lobsters, which are wearing little sombreros]
When Mr. Burns builds his casino and becomes obsessed with germs we get a real nice zoom in on Smithers’ face which is covered in germs. Then they say
“Freemasons run the country!”
I’m sorry, don’t quite follow.
Maybe you should see a doctor about that. When I blink I can still hear.
at the end of the episode where homer bans bart from seeing the itchy & scratchy movie it cuts to 20 years later and homer agreeing that bart can see it.
As they are going into the cinema homer spots something out of the corner of his eye…
homer: ooooh! Soylent Green!
Just as funny is Apu’s reply (said in a kind of exasperated, “not-again” tone of voice): “They’re in the safety cabinet, I’ll get the key.”
I think I’ve remembered my all-time favorite throwaway line. It’s from the Movementarians episode. Marge has just escaped their farm, and is running to find Rev. Lovejoy. We see him starting to douse the church with kerosene. He says:
“Never thought I’d have to do this again.”
I believe it’s:
I drink a whiskey drink
I drink a chocolate drink
And when I have to pee
I use the kitchen sink
I sing the song that reminds me I’m a urinating guy
Oh, and another of my favorites (from the halloween ep. with Dole and Clinton):
We must move forward, not backward; upward, not forward; and always twirling, twirling, twirling towards freedom!
In the Halloween episode based on the Shining, when the elevator doors open and the blood pours out Mr. Burns says, “That’s odd. The blood usually gets off at the second floor.”
Sorry, I spelled it wrong:
Nam myoho renge kyo translates somewhat as ‘Devotion to the Sutra of the Lotus Blossom of the Wonderful Law’. Buddhist mantra introduced in 1253… google-able for too much information. 
I guess i kind of like the obscure jokes- somehow the less accessible it is, the funnier it becomes. of course that means I’ve missed all the really funny ones myself, so that only holds up to a point…
How about the one where Lisa sees the movie that has the sexy mexican Lisa winning the dance contest. She then wins the heart of the smooth latin lover type guy. There is a mexican Milhouse character who then says:
“Once again, I must sugar my own churro”
Freaking hilarious!
Another one from the bible stories ep. After Homer has giving Flanders the Trojan horse, Ned remarks:
“Now whenever people get wood, they’ll think of Trojans!”
Bwaa ha ha ha
Welcome aboard(s), jormundgondir! Another Californian, woo hoo!
In the fat Homer episode there are two great lines.
The first Bart imagines himself as fat as Homer and says that he can only wash himself with “a rag on a stick”.
But the beat one was were Homer figures out that he can type “Y” instead of “yes” and says excitedly “I just tripled my productivity!”
As for the show getting old, one of the funnest episodes I’ve seen in a while was the show before the season finale where Homer gets his license suspended. All of the stuff in his car was hilarious!
one from bart’s future episode
Homer says something like
“mmm, soylent green”
then bart i think says
“Isn’t that made from people, hows it taste?”
Home responds
" It varies from person to person."
Actually, teemingOne, that latter quote is from Futurama.
Homer: I’m sorry, Bart; I didn’t realize that you and Jay Leno and a monkey were bathing a clown.
my bad, what was the joke about soylent green in the bart’s future episode then?
Old Homer [Upon noticing soylent green is sold at a movie theater’s concession stand): Mmmmmm, soylent green.
Homer is eating “Soylent green” cereal:
Bart: “Isn’t that people?”
Homer: “Oh, here we go…”
NDP - that other line is from the episode where Homer finally takes Bart to see the Itchy and Scratchy movie in the future, where Bart is now a Supreme Court Judge.
This leaves me rolling, but no one has ever quoted it to me. Not a great episode, perhaps?
Marge, when she was robbed at gunpoint and took up bodybuilding/steroids :
“I didn’t give up my period for second place!”