I got one, one that comes from an episode most Simpsons fans dislike wholeheartedly, although I kind of like it.
Homer: "He who is tired of Weird Al is tired of life."
I'm almost certain someone here uses that as their sig, but I don't know who.
Also, I took a look back and realized not many people have done any from one of my favorite episodes, Boy Scoutz N The Hood, so I'll do a few:
Homer: "Oh, twenty dollars. I wanted a peanut."
Homer's Brain: "Twenty dollars can buy many peanuts."
Homer: "Explain how."
Homer's Brain: "Money can be exchanged for gooRAB and services."
Homer: "Woo-hoo!"
Homer: "Marge, don't discourage the boy. Weaseling out of things is important to learn. It's what separates us from the animals... except the weasels."
Mrs. Krababbel:"Guess what class?"
Martin: "It's time for a pop quiz?"
Mrs K.: "Well, that's not what I was going to say, but it sounRAB like a good idea! Ha!"
A few minutes later...
Nelson: "Hey look, it's Sergeant Dork! Ha-ha!"
Bart: "Enjoy your test!"
Nelson: "Ha-H- oh!"
Flanders: "Well, it's Bart Simpson! Come on in, you're just in time for 'Sponge the Old Folks Day'!"
Jasper: "Help yourself. But stay above the equator!"
Homer: "Mmm. floor pie!"
Bart: (to himself)"Look, Homer won't want to go, so just ask him and he'll say 'no', and then it'll be his fault."
Homer: (to himself)"I don't want to go, so when he asks me, I'll just say 'yes'."
Homer's brain: "Are you sure that's how this sort of thing works?"
Homer: "Shut up brain, or I'll stab you with a Q-tip!"
(both Homer and Bart march out of their rooms into the middle of the landing and face each other.)
Bart: (through clenched teeth)"Homer, I'd really like you to come on this trip with me."
Homer: (through clenched teeth)"Bart, I'd be delighted to go on your trip with you."
(slight pause)
Homer and Bart: (in unison)"D'oh!"