The Sopranos: "Pine Barrens" is easily the best episode. Just fantastic all-round.
Fawlty Towers: "Gourmet Night", just for Basil attacking the car.
Frasier: "The Seal That Came To Dinner". A perfect blend of slapstick and wit.
Only Fools & Horses: "The Unlucky Winner Is...". This is the one where they go on holiday and Rodney has to prtend to be fourteen. It's just wonderful.
Father Ted: "Speed 3". Big pile of boxes in the road. 'Nuff said.
Peep Show: "Holiday". Everything just comes together in this one, and as things become more and more ridiculous, it all seems eminently plausible.
The Office (UK): "Training". Easily the best, in my opinion. As well as the hilarious Brent song, there's Gareth's perversions and the cringe-inducing end with Tim.
24: "Day 5, Episode 24". Charles Logan was my favourite 24 character, and this one came together beautifully. Great ending.
Lost: "Deus Ex Machina". The episode that made Locke into a truly tragic figure.
And finally, my favourite TV show ever...
The West Wing: So many, but I'll see if I can narrow it down to three.
"Noel." This one is basically a one-man show from Bradley Whitford, who plays the whole thing beautifully.
"Somebody's Going To Emergency, Somebody's Going To Jail". The storyline with Sam is beautifully done.
"Two Cathedrals". One critic called it the finest hour of television ever, and he's not far wrong. This is simply fantastic.
So apparently I've got three by the end of series two :-\. Fuck it, I'll keep going.
"Posse Comitatus". Both the main storylines in this episode are fantastic. It manages to focus on the characters while also bringing into focus much wider issues.
"20 Hours In America Parts I and II". Just for the Donna/Toby/Josh storyline, which is hilarious and touching.
"The Long Goodbye". A lot of people hate this episode, but I found it a refreshing change of pace and really heartwarming and heartbreaking.
"Life On Mars". I love me some Tim Matheson, and he's great here.
"Twenty-Five". Wonderful storyline, which had been hinted at way back in the first season. Plus John Goodman. 'Nuff said.
"Shutdown". Just a great storyline all round.
"No Exit". An hour of fantastic acting.
"A Change Is Gonna Come". Sets things up for the rest of the seasons very nicely.
"2162 Votes". So much happens in this one, and it's genuinely exciting.
"Here Today". As controversial as this storyline was, it's hard to deny that all the actors involved were terrific.
"The Debate". While clearly written to favour Santos, this was still wonderfully done.
"Institutional Memory". Since the last episode was kind of dull, this was the last quality episode of the show.
Well, that's 15 >_>