Damn, there are so many. Here're some I quote all the time...
"This bra bomb of yours better work Nerdlinger! Nyaiiiii!"
"Mmm, 64 slices of American Cheese. 64, 63..."
"Mmm, floor pie"
"I've hidden it, to find it, you'll have to decipher a series of clues, each more fiendish than the las..." "Found it!"
"You've dialed 911. If you know the name of the crime being committed, press 1!..." Bart punches in a bunch of numbers in frustration "You've selected Regicide, if you know the name of the King or Queen being murdered, press 1!"
"We can't bust heads like we used to, but we can tell old stories that go nowhere. Like the time I took the ferry to Shelbyvile..."
"Simpson, Homer Simpson, he's the greatest guy in history! From the, town of Springfield, he's about to hit a chestnut tree! Doh!!!!"
"I want to go to Mount SPLASH-more. Take me take me take me take me NOW! NOW NOW NOW NOW NOW!"
"Call Mr Plow, that's my name, that name again is Mr Plow!"
"Homer, I have someone here who wants to speak with you." "Batman?" "No, he's a scientist". "Batman's a scientist". "It's not Batman!"
"Homer, this is James Taylor". "Ahhh, former President James Taylor"
"Lousy Smarch weather"
And of course Homer and the store owner talking about frogurt: "that's good!", "that's bad!"