At that point I truly believed they were brother and sister. 
Xander: “Generally speaking, when scary things get scared, not good.”
But my favorite was when a demon was trying to recruit Willow as one of his minions. When she refused, he sighed and said, “Well, if you change your mind, here’s my token. Give me a summons.”
Nathan Fillion seems to get all the best lines. From the opening scene of End of Days (Buffy), as Buffy approaches the Slayer Axe, which is all stuck in stone sword-like:
CALEB: “So? You found it. Not impressed. 'Cause the question now, girly-girl, is can you pry it from solid rock before I come over there and…” (Buffy easily pulls it free) “Darn.”
I must’ve watched that scene fifty times, laughing every time. Fillion’s timing was perfect.
I like the moment just before that, when Jayne calls out “Is anybody there?” and River peeks around the corner.
Jayne: “Anybody else?”
Jayne all goofy before passing out was also hilarious.
And also: just about everything Wash ever said.
Another fantastic non-verbal moment, from Hush:
Buffy: makes quick downward movements with hand
Everyone looks on in shock.
Buffy: rolls eyes, reaches into purse, gets stake, repeats
Mal: Define ‘intersting’
Wash: (said matter-of-factly) Oh god oh god we’re all going to die.
The best part was Wash’s response.
‘So?’ (Which would, in fact, be my response if I were Wash, by the way.)
My favourite Harmony moment is the last episode of Angel.
After betraying him to the Senior Partners, and getting fired for that (not staked, mind, fired - Angel knew she was evil and didn’t blame her for it), she stands there while Angel faces off against Adam Baldwin’s character.
Harm: So…can I have a letter of reference?
Angel: Sure, it’s in my desk.
River. re Shepard Book’s hair: It’ll still be there. Waiting.
(Also, the whole bit earlier with her ‘fixing’ Book’s Bible.)
Which reminds me of another of my favorite exchanges…
Angel: People who don’t care about anything will never understand people who do.
Hamilton: True, but we won’t care.
Spike, watching Angel from above a rooftop:
“How can I thank you, you mysterious, black-clad hunk of a night thing? (low voice) No need, little lady, your tears of gratitude are enough for me. You see, I was once a badass vampire, but love and a pesky curse defanged me. Now I’m just a big, fluffy puppy with bad teeth. (Rachel steps closer to Angel, and Angel steps back warding her off with his hands) No, not the hair! Never the hair! (high voice) But there must be someway I can show my appreciation. (low voice) No, helping those in need’s my job, - and working up a load of sexual tension, and prancing away like a magnificent poof is truly thanks enough! (high voice) I understand. I have a nephew who is gay, so (low voice) Say no more. Evil’s still afoot! And I’m almost out of that Nancy-boy hair-gel that I like so much. Quickly, to the Angel-mobile, away!”
Yeah, that one never quite rang true for me. Any of us could say the same thing today. Here’s an example:
2007 Person A: That sounds like science fiction.
2007 Parson B: Honey, you have a telephone inside your ear/ a flat television hanging from your wall / a fireplace that starts itself / a robotic floor vacuum / ad infinitum.
Non one ever thinks of extant marvels as being science-ficitiony, even if they were so just a few years previous, so Zoe wouldn’t have said something like that.
[paraphrasing]
Xander: Why Willow? She was so much better than me.
Giles: Yes, she was.
Enter Willow
Willow: (Cheerily) Hi!
Everyone looks stunned
Willow: Geez! Who died? (pause) Oh my God! Who died???
:eek: Holy crap, we do live in science fiction!
Followed by “Hey, did you guys happen to do a whole bunch of drugs?”
Oh, my favourite Dopplegangland bit is after Willow met Vampy Will.
‘I think I was a little gay.’ Mildly amusing line at the time, her discomfort with the idea became a whole lot funnier when she hooked up with Tara…especially after ‘Hello! Gay now!’
I liked Spike summing up Giles entire life:
“Cuppa tea, cuppa tea, almost got shagged, cuppa tea.”
I always loved the opening scene from “The Puppet Show”
Cordelia puts the microphone back on its stand and leaves the stage as Lisa sets up with her tuba. Cut back to Giles as Lisa begins her tuba solo. Giles resignedly rubs his eyes and the bridge of his nose. Buffy, Willow and Xander come bouncing down the center aisle toward him.
Buffy: (draws a breath, teasing) If it isn’t the great producer!
They go into the seats and sit around Giles.
Xander: Had to see this to believe it.
Giles: (in a not at all welcoming greeting) Oh. You three.
Buffy: The school talent show. However did you finagle such a primo assignment?
Giles: Our new Fuhrer, Mr. Snyder.
Willow: I think they call ‘em ‘principals’ now.
Giles: Mm. He thought it would behoove me to have more contact with the students. I did try to explain that my vocational choice of librarian was a deliberate attempt to (draws a breath) minimize said contact, but, uh, he would have none of it.
Buffy: Giles, unto every generation is born one who must run the annual talentless show. You cannot escape your destiny.
Giles: If you had any shred of decency, you would have participated, or at least, um, helped.
Buffy: Nah! I think I’ll take on your traditional role… and watch!
Xander: And mock!
Willow: And laugh!
They all laugh.
Buffy: (overly dramatic) O-kay. I think maybe we better leave our Mr. Giles to this business he calls ‘show.’
The three of them get up and start back up the aisle. Principal Snyder is there waiting there for them.
Buffy: Principal Snyder!
Snyder: So. We think school events are stupid, and we think authority figures are to be made fun of.
Buffy: No! No, we don’t. W-unless you do.
Snyder: And we think our afternoon classes are optional. All three of you left campus yesterday.
Buffy: Yeah, but we were fighting a demon…
Snyder: Fighting?
Buffy: Not fighting.
Xander: No, we, uh, left to avoid fighting.
Snyder: Real anti-social types. You need to integrate into this school, people. (crosses his arms) I think I just found three eager new participants for the talent show.
Buffy: What?
Xander: No!
Willow: Please?
Snyder: I’ve been watching you three. Always getting into one scrape or another.
Buffy: Well, we’re really, really sorry, but about the talent show, pleeease, you can’t make us…
Snyder: (interrupts) My predecessor, Mr. Flutie, may have gone in for all that touchy-feely relating nonsense, but he was eaten. You’re in my world now. And Sunnydale has touched and felt for the last time.
He starts past them down toward the stage.
Xander: Can I just mention, that detention is a time-honored form of punishment?
Buffy nods vigorously in agreement.
Snyder (turns to face them): I know the three of you will come up with a wonderful act for the school to watch. And mock. And laugh. At.
He continues down to the stage. Xander can’t believe this. He points up to the heavens and signals with both index fingers in an imploring gesture, and then with resignation sits down in a seat.
Xander: No!
Buffy spaces out and moans. She goes back into Giles’ row, sits next to him and looks to him for sympathy. He has none to give, and tries to hide a smirk
A lot of Jayne’s funniest moments are visual, but I have to go with him fumbling his lines as Simon tries to coach him in his role as a paramedic for the hospital sacm, then snarling, “If I’d wanted schooling, I woulda gone to school!”. Then stoically delivering the hard-learned line to the receptionist despite her disinterest.
Buffy:You guys going to see Cibo Mato at the Bronze Tonight?
Willow: Cibo Matto’s Playing tonight?
Buffy: No they’re going to be clog dancing
Willow (Genuinely excited) Cibo Mato can clog dance? (Pause) oh
Giles: Feel up to some training?
Buffy: Sure, we could work-out after school, you know, if you’re not too busy having sex with my mother!
[Giles walks into a tree.]
Jayne: “Dear Diary: Today I was pompous and my sister was crazy. [flips page] Today we were kidnapped by hill folk, never to be seen again. It was the best day ever.”
Buffy: TV is good. Bright colors. Music. Tiiiiiiiiny little people!
Mal: One of you is gonna fall and die and I ain’t cleaning it up!
I came in to post Buffy’s, ah, ambiguous miming of staking a guy in “Hush,” but I see I was scooped.
So:
Buffy’s in the vulcanologist’s apartment, IIRC, and Angel comes to the door, slips, bumps into the jamb, and says eloquently, “Ow.” Buffy responds, “Stealthy!”
Zoe tells the Alliance interrogator that she and Wash are very private people. Cut to Wash waxing poetic about Zoe’s legs, “and where her legs meet her back [gestures] really that whole area . . .”
Giles as the Fyarl demon saying his car is “serviceable.”
Jayne getting doped by Simon has been mentioned, but Wash’s reaction is priceless: “Did he just go crazy then fall asleep?!”
Jayne and the Alliance mole - the whole dame scene. First when Mal tells him just to scare him: “Pain is scary.” Then lecturing the guy on his pathetic resistance to interrogation, wrapping up with a disappointed, “I was gonna get me an ear.”
Giles: She was truly the best of us.
Xander: She was way better than me.
Giles: Much, much better.
(“truly” may have been “surely” and " way" may have been “much”.)
There are too many for me to think of the best. One has a girl doing a butt-swinging dance at the Bronze.
Xander: Mmm, daddy like.
She turns around and they see that it’s Dawn.
Xander: No, daddy no!
Willow: I’m right there with you.