Larry Burns, when he is trying to sell souvenirs to the folks on the train to which Mr. Burns has attached his private rail car:
“Hey, if this stuff is too good for you folks, I’ve got some crap!”
And the Shelbyville kid talking to his friends after telling Bart to paint “Springfield Sucks” on a cliff in Shelbyville:
“That way, when people in Springfield look over here, they will know that they suck.”
(That last one may not be an exact quote, but it is isn’t exact, it should be pretty close.)
Along the same lines, Spoons, in the same episode:
Shelbyville Kid #1: How come we’ve never seen you in school?
Bart: I don’t go to school.
Shalbyville Kid #1: Yeah? What’s two plus two?
Bart: Five
Shelbyville Kid #2: Story checks out.
Man, that wasn’t just a “recycling place”, it was Uriah’s Heap.
**Interface, Eli, **and Spudo are all mentioning the same character, tho’ he doesn’t officially have a name. He is known as the wise guy.
I like the happiest man in town - “Not not me friends. He means himself; but thanks for looking”
:smack:
That’s supposed to be “No, not me…”
Homer: “Can I borrow a cup of sugar?” (paraphrasing)
Hank Scorpio: “Here ya go.” Pulls loose sugar from his front pants pockets. “Sorry it’s not in packets.”
Hank Scorpio is probably the best of the non-recurring characters. He’s my favorite, at least. 
Scorpio: Which country do you like more, Homer? Italy or France?
Homer: …Italy.
Scorpio: No one ever picks France. /aims the deathray
Another Mel Gibson line: I don’t want to attract any attention, so I’ll just go out in the alleyway and take a leak next to the dumpsters.
My all time favorite one-shot character is Cecil Terwilliger: You might experience a slight ringing in your ears. Fortunately, you will be nowhere near them.
Ahh, but you left out the best parts!
Another personal favorite, not yet listed:
When Homer shouts out his intentions to become an inventor to anyone within earshot of his window:
Sarcastic Man: DO US ALL A FAVOR AND INVENT YOURSELF SOME UNDERPANTS!
I use this line way, WAY more than I should in everyday life.
Grade 3 Teacher: Sobbing only raises Bart’s grade even more!
Woman: Telephone dear, it’s Homer Simpson.
Man: Tell him I’m not here.
Woman: He says that Ned Flanders is in trouble.
Man: Ned Flanders is in TROUBLE??
And I think the “I had a stroooooke” guy was also used as a worker at the toy store when Homer buys all the toys. So are they reusing the characters in order to appease the fans or because they’re lazy? 
Hank: Do you want any cream?
Homer: Errrr… No…
Not to be too nit picky, (and when I say that I intend to be totally nit picky) the guy I mentioned does not have a moustace, where as the wise guys always does. My guy just has a similar, if not the same, voice.
Why yes, I AM a Simpsons fanatic, how could you tell?