My all time favorite is the one where Kramer finds and rescuse the set of the old “Merve Griffin” TV show. He takes the stuff home and sets it up in his apartment, then interviews his “guests”.
Elaine: “Kramer, these chairs smell like garbage!”
Newman: “I’ve been buying the store brand of wax beans…they taste as good as the expensive ones”
Jack Hannah: “you isiot, squirrels are a hawk’s natural food!”
What’s yours?
Two words
MAN HANDS 
Everything else pales in comparison
Ugh. I can’t pick one, bu the Merv Griffin episode was great. Serenity Now?
NO SOUP for YOU!
I’m out.
I’ve been outed. I wasn’t even in!!
The Marine Biologist - it has the big payoff at the end.
The Fire.
“You made the stops?”
“They kept ringing the bell!”
Festivus.
“Many Christmases ago, I went to buy a doll for my son. I reached for the last one they had, but so did another man. As I rained blows upon him, I realized there had to be ANOTHER WAY!”
The Feats of Strength, the Airing of Grievances, it’s got it all.
The Parking Garage.
“Unbelievable. I’m never gonna get outta here. Guy goes to pee, he never comes back. It’s like a science-fiction story.”
“There’s too much urinary freedom in this society.”
“Why do I always have the feeling everyone’s doing something better than me on Saturday afternoon?”
The Bris. Between the twitchy mohel, George trying to get compensation from the hospital for a suicidal jumper landing on his car, and Kramer trying to hunt down the Pig Man, that episode has me in stitches from beginning to end.
This one. “Dovetailing” became the show’s signature, but a lot of the time the technique was forced and/or predictable. This was neither.
These are all great. The best part of the marine biologist episode is George telling the whale story. Equally funny is the episode where Kramer recounts how he tried returning the severed toe by taking the bus. (The one that StusBlues mentioned.)
I think my favorite episode is the one where Elaine hates the woman who “can’t spare a square”, who turns out not only to be Jerry’s girlfriend but Kramer’s phone sex operator. And Elaine is dating a mimbo that George has a man-crush on.
George Costanza: The sea was angry that day, my friends - like an old man trying to send back soup in a deli. I got about fifty feet out and suddenly the great beast appeared before me. I tell you he was ten stories high if he was a foot. As if sensing my presence, he let out a great bellow. I said, “Easy, big fella!” And then, as I watched him struggling, I realized that something was obstructing its breathing. From where I was standing, I could see directly into the eye of the great fish.
Jerry: Mammal.
George Costanza: Whatever.
Cosmo Kramer: Well, what did you do next?
George Costanza: Well then, from out of nowhere, a huge tidal wave lifted me, tossed me like a cork, and I found myself right on top of him - face to face with the blowhole. I could barely see from the waves crashing down upon me but I knew something was there. So I reached my hand in, felt around, and pulled out the obstruction.
[George reveals the obstruction to be a golf ball]
Cosmo Kramer: What is that, a Titleist?
[George nods]
Cosmo Kramer: Hole in one, huh?
The Opposite, where George does everything 180-degrees differently than what his impulses tell him to do. Also, Elaine buys jujyfruits (with disastrous results) and Kramer appears on Regis & Kathie Lee.
The Fire was actually the first Seinfeld episode I ever watched (I was too busy watching In Living Color over on FOX for the first couple seaons), so that still holds a warm place in my heart - George pushing down people to escape a tiny kitchen fire is what sold me on the show.
Overall, my favorite would have to be the trilogy of dinner party episodes (*The Dinner Party, The Rye, and The Stranded *) which I often mix up because they are 3 great episodes which all do basically the same thing – I crack up whenever I think about GORE-TEX, “I don’t drink wine, I drink PEPSI”, Beef-A-Rino, Saddam Hussein’s double parking, George with the fishing pole, and getting caught eating a pastry out of the garbage can (“so you said, what the hey, let’s eat some trash!”)
The most intriguing, is the girl who ALWAYS wore the same black and white dress.
I am still waiting to find out why.
Did she have 20, 30, 40 of the exact same dress?
Did she only own 1 dress?
Why couldnt Jerry after the break-up have continued to hand around her home/neighborhood and then observe what she was wearing?
My favorite was the one where Kramer went to work in the office.
I looked it up - its called The Bizarro Jerry, and it contains this exchange:
Hey George, can you feel this?
WAP WAP WAP WAP
Other than Elaine and his mother, I don’t think Jerry is particularly interested in women he’s not having sex with.
My favorite single episodes have already been mentioned, but I liked the whole arc that revolved around the series based on Jerry’s life.