The best:
Homer: Operator! Give me the number for 911!
The rest:
[Praying heavenward]
Homer: I'm not normally a religious man, but if you're up there, save me, Superman!
Homer: To alcohol! The cause of, and solution to, all of life's problems.
Homer: Weaseling out of things is important to learn. It's what separates us from the animals... except the weasel.
[Burns learns about the stock market crash of 1929]
Mr. Burns: Oh no! Smithers, why didn't you tell me about this market crash?
Smithers: Well, sir, it happened 25 years before I was born!
Mr. Burns: Oh, that's your excuse for everything!
Homer: I saw this in a movie about a bus that had to SPEED around a city, keeping its SPEED over fifty, and if its SPEED dropped, it would explode. I think it was called, "The Bus That Couldn't Slow Down."
[Bart's looking for his dog.]
Willy: Yeah, I bought your mutt -- and I 'ate 'im!
[Bart gasps.]
Willy: I 'ate 'is little face, I 'ate 'is guts, and I 'ate the way 'e's always barkin'! So I gave 'im to the church.
Bart: Ohhh, I see... you HATE him, so you gave him to the church.
Willy: Aye. I also 'ate the mess he left on me rug.
[Bart stares.]
Willy: Ya heard me!
Mr. Burns: We don't have to be adversaries, Homer. We both want a fair union contract.
Homer: [thinking] Why is Mr. Burns being so nice to me?
Mr. Burns: And if you scratch my back, I'll scratch yours.
Homer: [thinking] Wait a minute. Is he coming onto me?
Mr. Burns: I mean, if I should slip something into your pocket, what's the harm?
Homer: [thinking] My God! He *is* coming onto me!
Mr. Burns: After all, negotiations make strange bedfellows.
[chuckle]
Mr. Burns: [wink]
Homer: [thinking] Aaaaaagh!
[aloud]
Homer: Sorry, Mr. Burns, but I don't go in for these backdoor shenanigans. Sure, I'm flattered, maybe even a little curious, but the answer is no!
[While operating on Homer.]
Dr. Nick: [singing] The kneebone's connected to the... something. The something's connected to the... red thing. The red thing's connected to my wrist watch. ...Uh oh.
Homer: I am so smart! I am so smart! I am so smart! S-M-R-T! I mean, S-M-A-R-T!
Homer: Lisa, if you don't like your job you don't strike. You just go in every day and do it really half-assed? That's the American way.
Homer: Homer no function beer well without.
Homer: Kids, you tried your best and you failed miserably. The lesson is, never try.
Homer: Please don't eat me! I have a wife and kids. Eat them!
Pepi: Tell me more! I want to know ALL the constellations!
Homer: Well, that one's Jerry, the cowboy. And that big dipper-looking thing is Alan, the cowboy.
Gonna stop now, but could go on for days (and probably will, just not here)