I knew something bad would happen to Homer when he was ditching Moe’s car, but I had no idea that, after he jumped out of it while it was rolling down a steep hill towards a lake, that he would just roll onto a rock that would propel him right back into the driver’s seat.
The faint “boom” turned me into a lifelong fan.
Speaking of which: “Behold the Esquilax, a magical horse with the head of a rabbit and the body…of a rabbit!”
Similar to this, from the 101 Dalmations parody, Santa’s Little Helper’s girlfriend is having puppies, and the Simpsons are counting out the numerous births. “Twenty-two… twenty-three… twenty-four…” We see hours and hours pass on the clocks, and the family’s faces with looks of amazement. “…Twenty-five!”
Since some people have done non-Simpsons ones already, what about Family Guy? They’ve done that kind of joke dozens of times. (They actually ripped off the “person in disguise is really an identical twin” joke.)
In one episode, Peter* says “Man, I’m having the worst day ever. Has anybody else ever had a day this bad?”
(* Like most Family Guy cutaway jokes, I don’t remember which episode it’s from, who said it, or the exact wording, because it has nothing to do with the plot.)
Then it cuts to a Japanese guy walking to his car. A subtitle says “Hiroshima, 1945.” He picks up a parking ticket from his windshield and says “Oh, man! Could this day get any worse!?” Suddenly a shadow falls on him and you can hear a cartoonish falling whistle sound effect. The Japanese man looks up and says “Oh…my…god.”
Then a mandrill falls from the sky and starts beating him up.
Homer tries to jump Springfield Gorge and doesn’t make it so weget to see him tumbling down a cliff. The hoist getting him up keeps knocking him into the side of the cliff but finally he is safe in the ambulance.
The ambulance immediately runs into a tree, the back door opens, and Homer tumbles down the cliff again. That scene always cracks me up.
Homer has taken a free trampoline of of Krusty’s hands, but it’s caused too many injuries. Krusty won’t take it back, so he decides to drive to a canyon and push it off a cliff. We see it fall from above, the same angle as in the old Road Runner cartoons. Homer walks away and comments that he won’t be seeing that trampoline again. The trampoline falls on a large rock and springs back up the cliff, bouncing on Homer’s head over and over until Homer is lodged into the cliff. Homer comments to himself, “If this were a cartoon, the cliff would fall off now!” It doesn’t.
We dissolve to see night fall, and Homer is still lodged in the cliff. He feebly says to himself, “I’m thirsty.” And then the cliff falls off.
This one was one of my favorites as well. Always gets a laugh out of me…even right up until she says “Aaronson and Zykowski…”, she heaves a sigh of relief, like she’d been at it for hours. 
I’m watching Marge on the Lam now, and there were a couple in there that caught my attention. Marge and Ruth Powers approach a redneck bar that has the name spelled out across the front in large letters, but one of them is burned out. So from far away, it looks like “SH_TKICKERS”.
“Ooh,” Marge says, “I’ve heard a lot about Shotkickers.”
Then, inside, a good-sized man approaches her and makes a pass. “Feel like gettin’ lucky?” Marge responds that she is lucky, mentions her husband and kids, and thanks him for his attention.
“Listen, baby,” he says in a threatening tone, “I always get what I want.”
“I said ‘no’!” Marge clarifies.
He is suddenly apologetic. “Oh, did you? Oh, I completely misunderstood. Please accept our apologies.”
You thought that was the most egregious? What did you think of the infamous Rake Scene in Cape Feare? (Personally, I loved it.)
Speaking of the unexpected in comedy the gold standard is a scene in one of Chaplin’s shorts.
He plays a husband whose drinking is causing marital strife. His wife finally has had enough. She packs her bags and leaves him a note saying that she’s left him for good.
Charlie returns home and reads the note. In the next scene he has his back to us and we see his shoulders heaving up and down. It looks as if he’s sobbing uncontrollably.
The camera moves in and we think we see the punchline coming. Charlie will be seen to be laughing.
Then the camera reveals the truth. Charlie is shaking a cocktail mixer!
Pure comic genius.
Aaaaach! Zombie!
The “Beer Baron” episode where they test the catapult on the little kitten was hilarous… never saw that comming.
“I’ll give you this bottle of chloroform if you let me see the Who.”
To add from Family Guy:
there’s an espisode where Brian and Stewie are on the run from something. The standard scene of a bus pulling up which blocks our view of the characters happens, and we expect that when it pulls away the two characters will be gone. In fact, when it does pull away, they are gone, but they’re only down the road a little, and one of them says to the other, “We probably should have gotten on that bus.”
The alterate ending to “Who Shot Mr. Burns?”
“But for that ending to work, you have to ignore all the Simpson DNA evidence. And that would be downright nutty.”
In one of the Halloween episodes, where Bart wakes the dead, Homer shoots Flanders with his shotgun.
Lisa; “Dad, you shot the zombie Flanders!”
Homer: “Flanders was a zombie?”
I also love when he runs over Johnny and Edgar Winters.
The first South Park Christmas Episode, which introduces Mister Hankey.
There’s about three different times during the episode where Kenny is asked to do something insanely dangerous (climb a rickety ladder above a shark tank to take the star off the tree was one of them) and of course the audience expects him to die. The surprise is that Kenny actually survives to the end of the episode.
There is also the classic in the Lemon tree episode.
(paraphrased)
Bart(looking for the lemon tree or lemons): " Well I guess our plan was about about as useless as that yellow, lemon shaped rock over there…Wait a minute…"
“There’s a lemon behind that rock!”
Mine too. That, and “Wait a minute . . . that’s not the wallet inspector!”
Another from Oliver Beene.
In the nudie magazine episode (Oliver has stolen his dad’s nudie mag and then lost it). Earlier, Oliver and his lisping friend are playing I think “Untocuhables” and wearing the friend’s dads long trenchcoats. Later when they get the idea to pretend to be adults and go and buy a new copy of the magazine- You assume they will do the trenchcoat over the kid sitting on the other kids shoulders gag. Instead it cuts to the store and the two boys are wearing one of those two person horse costumes.
In that same episode:
In the car impound lot, an angry attack dog is chasing Bart. Homer tosses it a hunk of steak. We all expect it to either stop the persuit to go after the meat, or even possibly just ignore the meat all together. Instead, it catches and swallows the steak mid-stride.
“Quick boy! He’s got a taste for meat now!”