That would be “The Woman with Two Breasts”. I recently got the season 1 DVD as a present.
I agree with many of the others mentioned, namely “Love’s Labor Lost” and the subway episode of Homicide.
Some nominations based on the number of times I actually laughed out loud:
Friends: Where they play that game to see who knows more trivia about each other. (Actually, it’s MISS Chanandelar Bong)
Home Improvement: The one where Tim can’t get rid of that woodpecker.
Seinfeld: The one where Kramer adjusts his sleep cycle to match Lenoardo DaVinci’s.
Coach: For some reason the one that stands out in my mind is when Hayden, Christine, Kelly and Stuart go to a skid lodge for a weekend and Hayden gets locked outside when he is in the hot tub. The sequence where they come home and are looking around for him, and in the background all you see is him emerge from a mountain of bubbles and stiffly moves towards the door with the most contemptuous look on a face I have ever seen. I had to change my pants after that one 
Saved by the Bell: Ok, so when I watch them now all the jokes are cheesy and predictable, but the one that still makes me laugh is when they get fake marriages for a week in Home Economics class.
Lisa (daughter of Jessie and Slater): “I wan’t my own credit cards, phone and car.”
Slater: “You sound just like your mother.”
The Simpsons: The one where Bart ends up being the bartender for Fat Tony and his mob.
Marge: “I’m worried about Bart, but I don’t want to smother him.”
Homer: “Yeah, cuz then we would get the chair.”
Marge: “That’s not what I meant Homer.”
Homer: “Admit Marge, it is.”
South Park: The Chinpoko Man craze. That whole segment where the kids are watching the screen test for those commercials for alternative toys is genius.
“Wild-Wacky-Action Bike is nearly impossible to ride…but it glows in the dark!”
Is there an extended version of Once more, with feeling? The one i taped off tv is 45 minutes long and i don’t recognise one of the verses that was mentioned earlier, the one that buffy sings about the apocalypse and how they’ve been through it before etc.
The original airing was actually 1:10 (or so) in total length, with a bunch of snippets chopped out of later airings to fit within the one-hour timeslot.
I’m sure the full version will be (or is, since you’re in England) available on DVD.
Sigh. I never said I had a photographic memory.
“Banana cream pie.”
For me, hands down, no doubt, absolutely
Twin Peaks - The Pilot Episode
I wasn’t a David Lynch fan. I’d only seen BLUE VELVET and didn’t think much of it. I had friends who were interested and they talked about it, so I thought I should tune in just to know what they were talking about if they happened to mention it later. I turned the TV on and sat down at the computer, figuring I’d answer some e-mail while it was on (yes, we’ve been on the Internet since 1989).
At the opening notes of the the incredibly haunting music, I turned around, and stared at the TV. For the next two hours I was mesmerised, hypnotized and enthralled. Only movies in the theater had (and have) been able to make me feel that way. The only time I moved for the next 2 hours was from the computer chair to the couch, and by the end I was a besotted fan of David Lynch (who loves Blue Velvet now).
It was great being on the net then. It was years before anyone ever even thought about spam. There was no such thing as ads and popups (and, well, yeah, no world wide web either). The only time the real dickheads came out was in September and October, when a new school year started and idiots discovered they had net access. They were soon put in their place and usually didn’t cause any more trouble. Someone started the Usenet newsgroup alt.tv.twin-peaks, and it was great. If you didn’t get a reference, someone on the other side of the country got it and told everyone. Every inch of the episode (and all episodes thereafter) was analyzed and discussed. You didn’t have jerks just barging in opining that “Twin Peaks sucks man.” The people who were there really wanted to be there, and had to search to find it. Ah bliss.
Btw, I was one of those fans who stayed with it to the very end, and wanted to see it continue. A lot of people dropped out when The Answer (“who killed Laura Palmer?”) was revealed, but I never thought the show was mainly about Laura. It was mainly about the characters, the setting, the scenery, the places, the people, the bizarreness, the humor, the music, the silences, the red lights, the coffee, the whole ambience. An actual story (sometimes riveting, sometimes goofy, sometimes groan-worthy) was icing. Each episode was one day, which drove some people nuts when it got deep into the second season and the killer hadn’t been revealed, and I wanted to be there every single day, in this place, with these people.
The first season is on DVD now, but the Pilot episode, the one that started it all and is VITAL to understand the rest of the story, is locked up in a rights issue (if I had a rocket launcher…) and is only available as an import. Even then there are 2 versions. The European version is better than nothing, but they tacked on a terrible, nonsensical ending to release it theatrically. The much preferred broadcast version is available from Asia (as a real release, not a bootleg) and I finally found one. Hooray!
The Miami Vice ep where Brian Dennehy plays a TV evangelist.
The MASH** ep (originally 90 mins) where Trapp gets sent home, Hawkeye tries to catch him to say so long, BJ meets Hawk and Radar, they all travel back to the 4077th and have a lot of stuff happen, and when BJ meets Frank, he calls him Ferret face.
Tom Baker’s first Doctor Who
The Blackadder WW I hospital ep.
So many come to mind, it’s hard to choose one.
That’s “The Inner Light,” which, for those of you playing along at home, was my nominee. 
The monorail episode of the Simpsons.
The college episode of the Sopranos season 1.
The Newsradio episode “Super Karate Monkey Death Car.” “Feel my skills donkey donkey donkey donkey!”
The toupee and walnut episodes of the Dick Van Dyke show.
The first episode of Homicide, which made me think “Wow! This is way better than that other new cop show” (NYPD Blue)
The Boomtown episode about the stripper.
And Jose Chung, like others have said.
My nominees:
Seinfeld:
“The Contest”
“Not That There’s Anything Wrong With That”
“The Move”
“You’re Banned”
“Soup Nazi”
Cosby Show:
“The Birth of Twins”
“49th Anniversary”
“Theo’s Prom from Hell”
“Elvin In Dad’s PJ’s”
SVU
“Vigilante Justice”
Wonder Years
“First Kiss”
“Misdelivered Valentine”
I’ll think of more
Here’s my list:
PBS’s “Civil War” and “American Experiance: The Donnor Party”
Moonlighting’s “Atomic Shakespeare”
WKRP’s Thanksgiving episode where Carlson exclaims, “As God is my witness, I thought turkeys could fly”.
Fagjunk Theology: Not just for sodomite propagandists anymore.
Mystery Science Theather 3000: Hobgoblins. Bad '80s movie complete with bad '80 band, bad '80s special effects, and bad '80 sound effects (the rake fight scene) equals hilarity.
Hey Arnold: “Parents’ Day.” One of if not the best children’s shows out there. A very touching show.
Aqua Team Hunger Force- “Mooninites Revenge.” A belt that gives the wearer all powers of Foreigner. How can you go wrong?
Friends- “The One with the Free Porn.” Again, how can you go wrong?
I second the second-season finale of “Millennium,” and add the earlier second-season episode “Luminary,” which really begins the story arc of Frank’s schism and growing suspicion of the Group’s machinations. (Man oh man did third season ever drop the ball on that show.)
I will add a few to my previous pick.
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I second(or third?) Sleeping in Light from Babylon 5.
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The episode of The Office where everyone is playing jokes on people to raise money. David Brent dancing is a comic genius moment.
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The Germans or Hotel Inspectors from Fawlty Towers.
I’ll agree with both of those, and add in the series finale of Newhart, where Dick gets hit on the head with a golf ball and wakes up… well, I won’t spoil it, but if you’ve seen it you know what I’m talking about. Best series ending EVER.
There are a couple of episodes of Third Watch that stand out, namely “After Hours,” “September 10th” and the episode where Bobby dies.
**I can’t even read that without laughing out loud. 
Northern Exposure : Seoul Mates
NE always had a way of mixing two or three story lines together brilliantly and this one was one of their Christmas shows. The plots concerned Maurice finding out he had an illegitimate Korean son while Fleischman, a Jew, tries to celebrtae Christmas all intertwined with the local celebration of the Raven festival.
“My wish for you this Christmas? May your dog talk.”
I’m going to have to go with BtVS Fool For Love.
Everything about that episode (even the Riley scenes) were great. I don’t know much about the technical side of things, but I thought the whole episode was beautifully shot with wonderful camera work.
Plot wise? Fabulous. It clearly foreshadows Buffy’s sacrifice and lays groundwork for her death wish. It also foreshadows Riley’s departure, his inability to work with Buffy’s friends. It explores Spike’s past perfectly, and really rounded his character. A geek, an outsider, a poet, who–blossomed–into Spike. The tension between he and Angelus (and Angel), the obsession with the Slayers, the really hot Subway scene…
More than that though, it also explored his relationship with Buffy. I think the final scene, when he lowered the gun and asked if there was anything he could do was just brilliant. Then when he patted her on the back and the camera panned back and you realize, for better or worse, Spike had become her ally.
The** ER **episode when Mrk dies, love the way they had his letter posted up on the notice board and its winter and everyones complaining about the cold and stuff for part of the episode, and then we get a shot back to the main desk and susan is talking to someone else about the heat, clearly months have passed its now summertime, and the camera goes back to the letter as it falls off the wall and theres dust makrs all roun dit showing its been there a while, loved that effect!!
Also the last ever episode of Roswell just the fact that the gang were able to escape from Roswell and not be caught by the FBI, although personally would have prefered if UPN hadnt cancelled the show:mad:
I’ll third the Star Trek: TNG episode “The Inner Light” – excellent.
Also, this may be stretching the rules a bit, since it’s a three-parter, but Trilogy from Quantum Leap.