Ginny and Ron, being Weasleys, also get their share, but not nearly as many.
Any of Dumbledore's extremely eccentric but awesome ramblings, e.g.
Harry [to Hagrid]: You don't think anything that Skeeter cow -— sorry, Professor-
Dumbledore: I have gone temporarily deaf and haven't any idea what you said.
Harry: Errr... right.
Fred: YOU'RE JOKING!
Dumbledore: I am not joking, Mr. Weasley. Though now that you mention it, I did hear an excellent one over the summer about a troll, a hag, and a leprechaun who all go into a bar- (McGonagall clears her throat loudly)
Dumbledore: It's lucky it's dark. I haven't blushed so much since Madam Pomfrey told me she liked my new earmuffs.
At one point, Professor McGonagall slips on wet floor (Peeves' work) and catches the nearest thing for balance, which happens to be Hermione's neck.
Any time a character impersonates another via Polyjuice Potion (with the exception of Crouch Jr.) is made of hilarity. From the Crabbe and Goyle switch way back in Chamber of Secrets ("What are those?" "...Reading glasses." "I didn't know you could read."), to the Seven Potters, to the trio taking on ministry forms, especially Runcorn-Harry trudging awkwardly about in his leather coat, to Bellatrix-Hermione looking nervous and polite while trying to act haughty and cruel.
When Uncle Vernon is wrestling with Harry in the sea of letters and yelling about 'going far away where they can't find us', Dudley asks "Daddy's gone mad, hasn't he?" Petunia's only reply is a facial expression that just screams, 'Well, when you put it like that...'
When Hagrid knocks the door off its hinges in PS/SS: "Sorry 'bout that!"
When Hagrid accidentally tells them loads of information about the Stone. "I shouldn'ta told you that! I should not have told you that!"
"Troll in the dungeon!" scene. Especially the terror-stricken look on Malfoy's face.
The scene where Malfoy catches The Trio and Hagrid with a dragon. While its obvious the Trio are pissed off that Malfoy told on them, the look on Harry's face changes from angry to a Slasher Smile the second McGonagall says that Malfoy gets detention for the misdemeanor of being out at night with them.
...and the Chamber of Secrets
From the Chamber of Secrets film, while Harry and Ron are on the train. They're looking for it and are flying right on the tracks, when they hear the train's horn blowing. They can't see it in front of them and it's getting louder. Hedwig is the first one to look back, and when she sees the train is right behind them, her eyes widen. That entire scene is funny, right from the moment Harry and Ron slowly realize they aren't gaining on the train. And right after Hedwig reacts, it's the boys' turns. Their reaction? They SCREAM. And it lasts for a good 10 seconds!
Funniest line in the Harry Potter movies which wasn't in the books: After Harry and Ron are sent into the Forbidden Forest to "follow the spiders", Ron, who has a previously established fear of spiders, quips "Why spiders? Why couldn't it be 'follow the butterflies'?" Made even funnier by the director taking advantage of Rupert Grint's voice change hitting mid-movie. Yeah, that voice-cracking wasn't completely intentional.
In a Call Back to Chamber of Secrets, we have the scene in Prisoner of Azkaban, where Ron is having a nightmare:
Ron: "Spiders, Harry! They want me to tap dance. And I don't want to tap dance!"
Harry: "You tell those spiders, Ron."
And immediately afterward, muttering that he'll tell those spiders, he lays back down. As soon as his head touches his pillow, he's snoring again
In the Shrieking Shack:
Sirius: Pettigrew's alive! And he's right there! *points at Ron who's holding Scabbers/Pettigrew
Ron: Me? He's mental!
Sirius: Not you! Your rat!
The UST between Hermione and Ron in Prisoner of Azkaban. The first is during the lecture where Buckbeak is introduced and Hermione, in a panic, grabs Ron's hand. He proceeds to give her this amazed look, and she shoots him a glance that says "Don't you say a word". The second is when they're visiting the Shrieking Shack, and Hermione asks if he wants to get closer. After a short uncomfortable pause, she specifies that she meant closer to the shack.
The Knight Bus scene, especially Stan Shunpike's introduction.
Stan[sees Harry on the ground] What you doin' down there?
Harry I fell over.
Stan Whatcha fell ova for?
Harry I didn't do it on purpose!
Harry attacking Malfoy, Goyle and Crabbe with snowballs after they called Hermione a Mudblood. This includes throwing snowballs at them, causing Goyle's pants to fall down, and dragging Malfoy across the snow by his feet, all the while hiding under the invisibility cloak. Then after they retreat, Harry, still invisible, plays with Ron's hat and Hermione's hair before finally revealing himself.
...and the Goblet of Fire
Daniel Radcliffe's very good at being hilariously blunt. A good example being the final scene of Goblet Of Fire, where it's sinking in to Hermione that Voldemort is back.
Hermione (close to tears): "Everything's going to change, isn't it?"
Harry: (puts his hand on her shoulder, then says "Yeah" in a completely blunt, unsympathetic tone)
Ron complaining about Krum: "Ruddy pumpkinhead!"
Also Ron coming in pale and shaking and looking like he's about to faint because "He just asked Fleur Delacour out."
Harry (wearing a hilariously smug expression): Bubble juice, sir?
Snape lamenting that the Veritaserum's use on students is "regrettably forbidden."
The studying scene, where Harry and Ron keep on getting caught talking by Snape and get their heads smacked by a book and forced down for their troubles. The uber-annoyed look Snape gives and the precise manner in which he pulled up his sleeves before shoving their heads down was the icing on the funny cake.
Harry meets Rita Skeeter.
Harry: My eyes are not "glistening with the ghosts of my past"!
When Myrtle gets in the tub with Harry.
Neville gives Harry gilliweed for the second task which takes place underwater. When he doesn't appear to surface after a few minutes. Neville turns around grabbing the sides of his head in a panic "Oh my God! I've killed Harry Potter!"
Honorable Mention goes to the deleted scene in which the Hogwarts students sing their house song. Harry and Ron look embarrassed, Crabbe is really getting into it while Draco cringes behind him, and the students from the other schools look... uncomfortable. Oh, and did we mention that there's hand motions with the song?
When Ginny is dragging Ron back into the common room, half in shock...
Ginny: He just asked Fleur Delacour out.
Harry: What did she say?
Hermione: No of course.
Ron shakes his head.
Hermione: She said yes!?
Ron: There she was walking... (dreamily) you know how I like it when they walk. And it just... slipped out.
Ginny: Actually he sort of screamed at her. It was a bit frightening.
The playful teasing that the rest of the group gives Ron as he's raving about Victor Krum, culminating in everyone breaking out into song.
Ron: He's more than an athlete, he's an artist.
Ginny: I think you're in love, Ron.
Ron: Shut up.
Fred: Victor I love you.
George: Victor I do.
Fred, George, and Harry: When we're apart, my heart beats only for you!
Harry, Fred, and George's reactions to seeing Ron being forced to dance with McGonagall.
Words cannot describe the hilarity of Harry telling Cormac McLaggen that the appetizer he just put in his mouth was dragon balls ("Dragon...balls?"). Which he promptly sicks up onto the shoes of Severus Snape. Who puts McLaggen in detention!
McLaggen flirting with Hermoine. By licking his fingers.
Harry coming back to the feast after being sneak attacked by Malfoy.
The scene where Ron is in the hospital wing after being poisoned, and his annoying girlfriend Lavender comes in worried and asking "Where's my Won-Won?" She and Hermione get into a fight over him, where Hermione calls her a "daft dimbo"! What makes this even funnier is that it's happening in front of the teachers — Dumbledore, McGonagall, Slughorn, and Snape. Then Ron calls out Hermione's name in his sleep, and Lavender runs off crying; Dumbledore quips "Oh, to be young and to feel love's keen sting!" While McGonagall and Snape keep their cool after Lavender storms off, Dumbledore is the only one who turns to look at her. Snape just stares straight ahead during that scene. It also becomes a little funny and sad once you realize that he should know how Lavender feels...
What really settles it is the dialogue! No, seriously, it's bloody hilarious:
Lavender: Where is he? Where's my Won-Won? Has he been asking for me? ...What's SHE doing here?!
The whole bit with Slughorn sneakily cutting a leaf from a plant in the greenhouse when Harry walking into frame in the background, turning and seeing him and getting right next to him without saying anything and Slughorn getting the crap scared out of him when he turns his head!
When Harry and Dumbledore are about to leave for the cave:
Harry: But sir, I thought you couldn't Apparate in Hogwarts.
Dumbledore: Well, being me definitely has its advantages.
Ginny and Harry share their first kiss inside the Room of Requirement. Aww. Immediately cut to...
Ron: Did you and Ginny do it, then?
...and the Deathly Hallows
Harry is still at the Burrow and instigates some snogging with Ginny. And who walks in to get a cup of tea but George. He sits back and watches the show, and soon enough, both of them know he's there. Cue deadpan stare from George with knowing grin just sipping his tea, telling the two, "Morning." The theater erupted in laughter. The scene is made all the more funnier due to George going through the whole thing with a toothbrush stuck to the side of his head. Check out his rapid-fire tip-toeing too.
In my opinion, it's even more hilarious that Harry's still scared of what George might do to him, even though George is being good-natured about the whole thing. Notice how Harry never completely turns his back to George, and when he finally does, he runs like hell?
Mad-Eye: Now, for those of you who have never tried Polyjuice Potion, it tastes roughly like goblin piss.
Fred: You'd know all about that, wouldn't you, Mad-Eye? [awkward silence]* Just trying to relieve the tension.
The look on Fred's face and his tone of voice just makes it funnier.
Mad-Eye (about Harry): "Yeah, he's absolutely gorgeous. Now what's say we get him undercover before someone murders him!"
Harry's little jump of joy after Hermoine said they should go to Godric's Hollow.
Mrs. Cattermole kissing Ron, who's Polyjuiced as her husband. Also Hermione's "WTF?" reaction, Ron turning back to his original form while their lips are locked, and her real husband showing up in his underwear!
After Yaxley reveals to Polyjuiced Ron that Mrs. Cattermole is being interrogated, we get this:
Ron: Oh my God! What am I going to do!? My wife's all alone downstairs!
Harry: ...Ron, you don't have a wife.
Ron: Oh. Right.
Hilarious in Hindsight, since Ron's eventual wife, Hermione (and everyone who's completed the corresponding book knows this already), is indeed downstairs, disguised as Mafalda Hopkirk.
Yaxely: "It's still raining in my office!"
Ron: "Have you tried an umbrella?"
Especially hilarious is the subtle Brick Joke concerning the flooded office later, when Ron steps back on the elevator completely drenched with water, implying how much success he had with reversing it.
The deleted version of that second scene, where Arthur Weasley and one of his coworkers get in the elevator with Ron and Harry.
Witch: Don't tell me, it's raining in Yaxley's office again?
Arthur: Did you tell him to try an umbrella?
After finally destroying the evil Horcrux that nearly killed them: Ron: "Just think. Only three more to go!"
After Ron returns, his "Hey!" and Hermione's reaction to it is priceless.
Fred (or George) about Polyjuicing into Harry: "Suppose something went wrong and we wound up a scrawny, specky git forever!
Runcorn-Harry's expression when Umbridge says "Albert, aren't you getting off?" and the ridiculous way he walks off the elevator. And the ridiculous way he walks out of Umbridge's office.
"What's wrong with his face?"
Scabior to Harry: "What happened to you, ugly?" (beat) (to Greyback) "No, not you."
Ron giving Harry a new wand. "It's ten inches. Nothing special, but it does the job."
Kreacher and Dobby dragging Mundungus in. And Dobby pushing Kreacher out of the way every time he tried to talk. And Kreacher jabbing Mundungus with a fork.
Voldy's line: "Severus, I was beginning to worry you'd lost your way. We've saved you a seat" just cracks me up, because you can just hear by the tone that what he's really saying is "show up late again and I'll Crucio your ass into next week!"
Voldemort's response to Thicknesse after the latter is suitably vague in whether he believes Yaxley's report on Harry's imminent escape from his house or Snape's: "Spoken like a true politician." Voldy is surprisingly humorous, particularly considering the murder of Charity Burbage at the end of the scene.
When Voldemort learns of the plan to move Harry, Bellatrix starts fidgeting in her seat raising her hand to volunteer, like Hermione trying to get a teacher's attention...
In Part 2, McGonagall animates the stone knights to defend Hogwarts and then, with all the excitement of a first year just arriving at Hogwarts, gleefully says, "I've always wanted to use that spell!" Made all the more priceless by Molly's expression. It positively screams, "...really?"
Part 2, Voldemort's INCREDIBLY awkward attempt at hugging Draco following what he believes is his final victory. He simply has no idea what he's doing. And Draco looks so terrified too. He looks ready to wet himself. Adding to the hilarity is the way Dean is smirking, clearly suppressing laughter.
It was a different kind of hilarious. Some even said "Eww".
There's even a Facebook page for it now: "That awkward moment when Voldemort hugs you."
Also from Part 2, Neville taunting the onrushing Death Eater army after they hit the defensive barrier. And then his Oh Crap reaction after the barrier is eventually neutralized.
In Part 2, after Hermione drinks the Polyjuice Potion to look like Bellatrix:
Hermione: "How do I look?"
Helena Bonham Carter's performance during that entire sequence is such a hilarious contrast to how she usually is in these movies.
It gets even funnier when you go meta. Helena Bonham Carter worked with Emma Watson on those scenes, with Watson acting out the scene, and then Carter mimicking her. So, in essence, you have Helena Bonham Carter pretending to be Emma Watson pretending to be Helena Bonham Carter pretending to be Hermione pretending to be Bellatrix. Your head may now explode.
When McGonagall starts getting the school into defense mode and she tells Neville he can go blow up the bridge:
Neville: You're actually giving us permission to do this?
McGonagall: That is correct, Longbottom!
Neville: To blow it up? Boom?
And then immediately after that, Neville asks how they're going to blow it up:
This entire exchange had the whole theater in stitches.
The look of absolute glee on McGonagall's face after making the giant statues move. "I've always wanted to do that spell!"
Neville calmly regaining consciousness in slow motion while the battle rages on behind him, looking a little punch drunk, but otherwise pretty nonchalant. Not only is the Battle of Hogwarts raging on in the background, there is a guy flying through the air, in slow-motion, on fire, while Neville looks like he was getting up from a nap.
Filch running in screaming "STUDENTS IN THE HALLS! STUDENTS OUT OF BEDS!!!" He bursts into the Great Hall, packed with students and teachers. Everyone just gives him a deadpan stare, which just screams "You idiot." He takes a step back from all the concentrated vehemence, complete with a little "...Oh."
McGonagall: They're supposed to be, you blithering idiot!
In a wonderful Funny Background Event, after all the dust has settled, Filch can be seen trying to clean up the massive amount of rubble and debris that much of Hogwarts has been reduced to... with a push broom and an expression that seems to say "Welp.... better get started.
Pansy Parkinson's hysterical "What are you waiting for? He's standing over there! Somebody grab him!" In the books the narration portrays her as a bitch but in the movie, she seems to be a random Slytherin girl which makes it more funny.
In DH:P1, during the scene in Malfoy Manor when Harry and Ron go to rescue Hermione, and the fight breaks out. Lucius draws his wand-cane - and then stares at the wandless handle for a second before he gets stunned, because Voldemort took it at the beginning of the movie.
Harry: Since when have any of our plans actually worked? We plan, we get there, all hell breaks loose.
Made even more hilarious when you consider that in the book, they literally spend months planning stuff and wandering about trying to figure out what to do, and when they do get around to doing something, everything goes to shit and loads of stuff starts to happen all at once.
The fact that in the later movies, Draco becomes a sorta pedobear magnet... and he does not like it one bit. In DH 1, in the manor his Dad's then his Aunty's all whispering in his ear all creepy-like and he looks like he's about to cry. Even Voldy gets in on the Perv On Dracokins action in the next film. Creepy ass hug anyone? I think it's safe to say Draco's the resident bitch in the Death Eaters.
In Deathly Hallows, Hermione is about to read aloud the Tale of Beedle the Bard, when Ron awkwardly interjects before she starts. As the camera pans out of the Lovegood house and into the animated sequence following a floating feather, we get Ron and Hermoine's lines off-screen, making them sound like an old married couple:
Hermoine: ... do you want to read it?
Ron: N-no... no.
Harry has an important mission for the D.A.:
Harry: Okay, there's something we need to find, something hidden here in the castle, and it may help us defeat You-Know-Who. Neville: Right, what is it? Harry: We don't know. Dean: Where is it? Harry: We don't know that either. I realize that's not much to go on. Seamus: That's nothing to go on.
After The Trio get back to Hogwarts, Ginny breaks through the crowd in the Room of Requirement and Harry and Ginny just stare at each other
Ron: I just get back and she looks at me like I'm a franky first-year
Seamus: She's got plenty of those though. There's only one Harry.
Ron: Shut up, Seamus.
Ron chasing after the Terrible Trio in the Room of Requirement, yelling "THAT'S MY GIRLFRIEND, YOU NUMPTY!" after Goyle attempts to use Avada Kedavra against Hermione.
Then a minute later a panicked Ron running back yelling "GOYLE SET THE BLOODY PLACE ON FIRE!", grabbing Hermione and leaving Harry!
"NOT MY DAUGHTER YOU BITCH!"
The moment where Voldemort announces "Harry Potter is DEAD!" and follows it with an absolutely ridiculous "HEH HEH HEH..." One of the funniest moments in DH Part 2, it's so awkwardly done, it's reached Memetic status. Four movies worth of Voldemort's characterization completely fell flat on its face right there.
This troper finds the fact that Snape sticks his thumbs out of his pockets hilarious.
In the PC version of Chamber of Secrets, when you get hit by Mimblewimble, it can be amusing when Harry yells the spell name incorrectly.
In the Game Boy Color version of Chamber of Secrets, if you turn the language to Spanish, the first time you enter Ginny's bedroom, you'll walk in on her experimenting with ways to say "Mrs. Ginny Potter".
Ron gets really over-excited about pointing out Bertie Bott's Beans when they appear in Goblet of Fire, to the point that Hermione expresses her annoyance at him for this.
Ron: "Oh look, a bean!"/"You know, I really love beans."
Hermione: "Thank you for pointing out the obvious, Ronald."/"Will you stop going on about beans, Ron!"
Several in The Half Blood Prince. Early on, we have Ron doing an impression of a fish under the influence of love potion.
"Hermione, blub blub, I love you, blub blub."
Harry has just made a potion for Ginny's homework. There's a majestic score and Harry says they can now go to Hogsmeade together. Then Ginny says she's going with Dean Thomas. Cue Record Scratch.
When confronting Crabbe and Goyle,
Crabbe or Goyle: "What do you want, Potter"
Harry: "A moron free view? Oh, too late!"
When Harry is under the influence of Felix Felicis, we get treated to an upbeat jazz version of Hedwig's Theme, making it even more awesome. And the way he just strides around in that overly cocky way.