And since I know have my Simpsons bible here are a few things I found on the episode pages.
The Shelbyville Daily has a banner that reads "once a week, every week".
We find out that the towns originally split because Shelbyville Manhattan wanted to marry his attractive cousins and Jebediah Springfield wouldn't allow it.
Jebediah Springfield: People, our search is over! On this site we shall build a new town where we can worship freely, govern justly, and grow vast fields of hemp for making rope and blankets.
Shelbyville Manhattan: Yes! And marry our cousins.
Jebediah Springfield: I was- wha... what are you talking about, Shelbyville? Why would we want to marry our cousins?
Shelbyville Manhattan: Because they're so attractive. I... I thought that was the whole point of this journey.
Jebediah Springfield: Absolutely not!
Shelbyville Manhattan: I tell you, I won't live in a town that robs men of the right to marry their cousins!
And of course classic quotes:
Ned Flanders: Pardon me, neighbourinos. Some of our boys are lost in your town. You wouldn't have happenned to see them, by any chance?
Shelbyvillian #1: Sounds like Springfield's got a discipline problem.
Shelbyvillian #2: Maybe that's why we beat them at football nearly half the time.
Homer: That tree's been in Springfield since the time of our forefathers. Give it back or we'll bust in there and take it!
Shelby's Dad: Bust in here and take it? You must be stupider than you look.
Homer: Stupider like a fox!
At home, Marge vacuums under Homer's feet.
Marge: Where are you going, Bart?
Bart: Mom, you won't believe this, but something you said the other
day really got through to me.
Marge: [
happy] Mmm!
Bart: And now, I am going to teach some kids a lesson. [
slams door]
Marge: I choose to take that literally.
Bart: [
outside] Death to Shelbyville!
Homer: Yes, Bart's a tutor now. Tute on, son! Tute on.
This entire sequence is amazing:
Ned: OK, folks, look: I called the police captain in Shelbyville.
He says he hasn't seen our kids, but if they show up in the
morgue, he'll fax us.
Mr. Van H: Oh, man, I _hate_ those Shelbyville jerks.
Mrs. Van H: Honey, _I_ was born in Shelbyville.
Mr. Van H: And it tears me up inside!
Marge: This is my fault. I tried to teach Bart about town pride,
but the power of my words filled him with a sort of madness.
Homer: Now, Marge, you can't blame all of Bart's problems on your
one little speech. If anything turned him bad, it's that
time you let him wear a bathing suit instead of underwear.
_And_ let's not forget your little speech!
Marge: Isn't there anything we can do?
Homer: Yes there is! Come on, everybody, let's go into Shelbyville
and get those kids back ourselves. I got an RV we can use:
Flanderses!
Everyone: Yay! Let's do it. etc.
Flanders: Well, OK, but you know, just go a little bit easy on --
Homer: Pile in, everybody. No time to wipe your feet.