From Reverend Lovejoy: ". . . be they Christian (looks at Ned and family), Jew (looks at Krusty) or miscellaneous (looks at Apu)." Then Apu: "Hindu. There are 700 million of us!"
And I show the Homer^3 part of Treehouse of Horror VI every semester I teach physics II--it's great for black holes and general relativity. And the episode where Lisa decides to combat light pollution for the astronomy class when we do the chapter on telescopes.
Yeah...I can't really narrow it down to a favorite. Here are a few gems off the top of my head:
Homer: Is this a religious thing?
Krusty: A religious clown thing, yes.
Marge: Is this how you pictured married life?
Homer: Pretty much. Except we drove around in a van solving mysteries.
Mr. Burns (to an inspection team): There must be some mistake. We make cookies here. Mr. Burns' old-fashioned good time extra chewy ....
Lisa: Does this family know any songs that aren't commercials?
Simpsons: I feel like chicken tonight! Like chicken tonight! Like chicken tonight!
Homer: Ah, your flesh mother used to bring me pudding.
Rev Lovejoy: I will now read the special vows which Homer has prepared. Marge, will you take Homer in richness and in poorness -- poorness is underlined -- in quiet solitude or blasting across the alkali flats in a jet-powered, monkey-navigated . . . and it goes on like this.
"hey Fat Tony, I know you've been selling drugs at the high school but I'm willing to look the other way. IF you'll agree to go to my son Ralph's birthday party on Saturday. It'll be a lot of fun! Batman will be there..."