Yay! Someone mentioned this episode! I’m a rabid Smashing Pumpkins fan, so I loved this one.
Anyone remember the “Tappa tappa tappa” one where Lisa tried to learn how to tap dance? That one is one of the best.
“A Sound of Thunder,” by Ray Bradbury. The spoof was hilarious.
On the off chance anybody might need a citation for any of these quotes, the best place to start is The Simpsons Archive.
Oh, I LOVED the Bart is Gay one…“So John, this is your sick mother?” “Waylon, don’t do this.”
The Spin Off one, and the one where Sideshow Bob actually HELPS Bart and Lisa against his brother-ironically named Cecil.
“Homer, if you could kill a couple of soldiers on the way out, that would be great.”
“I didn’t fill my shoes with blood tapping code for the Allies in WWII for nothing, missy!”
When Homer went back to college to get his degree and he tries to prank call the Dean…
Homer: in disguised voice Hello, Dean? You are a stupid head!
Dean: Looks out window, sees Homer standing by payphone Homer, is that you?
Homer: AAAH!!
Also the one where Shelbyville spiked Springfield’s water supply…
Marge: Oooo, the walls are melting again!
Turkey: Frankley, I think I’m overdone
Mmmmmmm…forbidden donut… 
In Australia, on paytv, on a channel called Fox8… There has been a Simpsons Fanfest; Simpsons Episodes 24 hours a day from September 15th to October 1st.
If I could stay awake for about 360 hours I would watch them all, but alas I am not a god… 
I bet you all wish you lived in Auustralia??
PerfectDark
I just adore the song “See My Vest” I loved the disney versions and my friend Richard sings the parody just oh so wonderfully.
Kitty
For me it’s gotta be either the toaster/time machine one a few people have already mentioned or the one where Homer works for the evil villain Scorpio.
I love that part where “James Bund” flips the quarter into the air, splitting the laser beam into four parts that burn through each of the manacles restraining him.
I decided to wait until there were enough listed so I’d only have to pick among the ones not listed yet.
This instant, I might have to pick the one where Homer’s accused of sexual harrassment, with the candy convention, the “Under the Sea” parody, the Rock Bottom interview, a special episode of Gentle Ben, homemade Prozac, and Dennis Franz in Homer S.: Portrait of an Ass-Grabber.
Kent Brockman: Simpson scandal update: Homer sleeps nude in an oxygen tent which he believes gives him sexual powers.
Homer: Hey – that’s a half-truth!
One of my favorite Simpson quotes is from the Hullabalooza episode. Homer tells Billy Corgan, “Thanks to your gloomy music, my children have stopped dreaming of a future I can’t possibly provide!”
My personal fave has already been mentioned: the one where Marge is Blanche in “Oh, Streetcar!” The songs are hysterical. “New Orleans! Nasty, stinking vomitous bile, New Orleans!” and “You can always depend on the kindness of strangers…a stranger’s just a friend you haven’t met - Streetcar!” And the Ayn Rand Day Care Center is just great.
Additionally, I love every episode with Rev. Lovejoy. He’s probably my favorite minor character. Well, and Dr. Nick. And Troy McClure.
Rev. Lovejoy: Marge, perhaps you should think about getting a divorce.
Marge: But Reverend, doesn’t the Bible say divorce is wrong?
Rev.: Well, Marge, the Bible says pretty much everything is wrong.
Oh! And my other favorite episode: the one where Selma marries Troy McClure in a sham marriage solely because of “Planet of the Apes The Musical.” “I hate every ape I see, from chimpan-a to chimpan-z. You’ll never make a monkey out of me!” Statue of Liberty rises from the stage… “Oh my god, I was wrong, it was earth all along. You’ve finally made a monkey out of me! Dr. Zaius, I love you!”
“What is the BEST Simpsons episode of all time?”
You might as well ask someone which child is your favorite?
It’s just so damn hard to choose. But a quote does come to mind from the episode where they go to Australia:
Homer: Burkina Faso? Disputed Zone? Who called all these weird places?
Brain: Quiet, it might be you! I can’t remember.
Homer: Naw, I’m going to ask Marge.
Brain: No, no! Why embarrass us both? Just write a check and I’ll release some more endorphins.
[Homer scribbles a check, then sighs with pleasure]
I wish I could bargain with my brain like that.
the ‘mr. sparkle’ commercial is pretty dang funny.
my favorite whole episode is the one where homer goes to clown college. the clown music that plays while he’s obsessing about the clown college billboard is pretty creepy, especially when the dancing clowns he sees is actually his coworkers on fire. this one is great all the way to the end when krusty finally pays the mob boss the money he owes them and the boss says ‘and here’s a-your change, and a-we thank you.’
Ah, my heart sings whenever Joe Mantegna shows up as Fat Tony. I especially like him in the episode where Marge starts up a pretzel business and Homer buys protection from the mob. Great scene when Tony and his cronies stop Marge on the highway and Tony reaches into the car to take Marges keys from the ignition:
“Um…is there a button or something to release these keys?”
“No, you have to push it in and then turn it.”
Best episode is way too hard to pick, but I have a new favorite Homer quote:
“I’m the luckiest man in the world…now that Lou Gehrig’s dead.”
http://www.angelfire.com/indie/brainingdamage
come for the fish, stay for the fun
I’ve got over 225 Simpson’s episodes on tape. Picking the one best episode is not easy. Some of my favorites that haven’t been mentioned yet:
Mr. Burns for Governor
Homer Grows Hair
Marge Meets Jacques
Timmy in the Well
Lurleen Lumpkin (If I had to pick my favorite one this might be it.)