“Lovely Jubbly”: I have no idea if this was a genuine East End expression before Del Boy popularized it, but I still use it.
A more recent one I’ve started to use: “What the What” from 30 Rock when I’m completely baffled. An advantage is that nobody I know, despite my prodding, actually watches *30 Rock * so I have my own private in-joke.
Some aren’t sitcoms, but…
“I love it when a plan comes together.” - The A Team
“You might, rabbit, you might” - The gangster on some Bugs Bunny cartoon
“Underpants…underpants…underpants…” - Chobits
“Ooklah! Ariel! Ride!” - Thundarr the Barbarian
“Right turn, Clyde” - Any Which Way but Loose, whenever I’m a passenger giving directions.
“Bear left. Frog right” - Muppet Movie, also used whenever I’m a passenger giving directions.
“Who shot who in the what now?” Said by Jasper on The Simpsons. Used when I am totally confused about anything.
Call Ron and ask him if Janice spoke to Herb about the closing Fred is doing for Maxine?
Who shot who in what now?
When my wife asks me, “What did you do today?”, I often reply, “Same thing I do every day, Pinky.” I don’t always add “…Plan to take over the wooooorld!”, but I do sometimes.
I feel like I inspired this thread…
a la Homer being asked what his middle name is when he tried to impersonated Mr. Burns: I don’t know. (Requires proper vocal inflection)
When asked to “run” somewhere: I choose not to run (Seinfeld)
Another from the Simpsons requiring inflection: Rhetorical, eh?
I often throw a line from Homer J. here and there but I can’t think of any offhand right now… d’oh!
That’s because you did! 
After a calamity:
“I thought turkeys could fly!”
“That boy’s not right.” - Hank Hill
“That’s what she said.” (I know it didn’t originate with The Office, but it’s popularity has surged because of it)
“SERENITY NOW!”
“Shiny!” (not a sitcom, but usually a funny show)
From Father Ted:
Gwan, gwan gwan.
Feck! Arse! Drink! Girls!
Careful now. Down with that sort of thing.
Python:
It’s not dead, it’s pining for the fjords.
No-one expects the Spanish Inquisition!
And now for something completely different.
There are others, I’m sure.
I use these:
I also often say frell instead of the other f word, but that’s mostly like saying sugar instead of shit.
Purple Monkey Dishwasher
edit: didn’t originate on the Simpsons like I thought it had, but I’m listing it anyways, cuz I hadn’t heard of it 'till then.
The first isn’t really a sitcom, and the second isn’t really a catchphrase, but I use these quotes more often than I should:
“You knew the job was dangerous when you took it, Fred” (when someone complains about a task that is difficult or unusual)
“There’s your answer, fishbulb” (after someone has found an answer to a question, usually one they keep pointing out they want to find the answer to)
From Scrubs : “Say it !” (to which of course the other is supposed to dejectedly and mirthlessly reply “I’m your beeatch…”)
From Poirot : “I have been BLIND !” (in a heavy Fre…Belgian accent)
From House : “Iiiiiinteresting…” (in a sarcastic, Wilson way)
Is anyone here a marine biologist?
Sex…to *save *the friendship.
He’s a close talker.
She’s a low talker.
People…they’re the worst.
Oh, you don’t want people calling you at home? Now you know how I feel!
Something’s missing all right.
Whenever two of my friends are arguing, and someone makes a point that wins the argument I spout a little known line from the immortal Rocko’s Modern Life
Heffer (me): Oooop s/he got ya there rock!
(In case you are wondering it is the spring cleaning episode)
“It’s a perfectly cromulent word”
Another Futurama-ism: “Sweet zombie Jesus!” (although my wife really wishes I wouldn’t use it).
As an aside, I saw a Futurama rerun recently where this was bleeped.
Heh…on Easter this year, supervenusfreak wished me a Happy Zombie Jesus Day! And I replied, “Souls! Soooooouls!”
“These pretzels are making me thirsty!”
I use (from the movies):
‘Could be worse. Could be raining.’ -Young Frankenstein
‘Oh Fuddddddddddddddgggggggggggggge.’ The Christmas Story