Several from the Serenity movie, which is quite quotable:
Jayne: "Shiny. Let's be bad guys."
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Mal: "Kaylee, this is a place of business. We can talk about Simon-"
Kaylee: "When he's four worlds away? Or the Alliance gets ahold of him and River?"
Mal: "That ain't my worry. I gotta finish this job, get us another one. Can't do that carryin' those two."
Kaylee: "How can you be so cold?"
Zoe: "Cap'n didn't make them fugitives."
Kaylee: "But he coulda made 'em family. 'stead of keepin' Simon from seein' I was there. And I carried such a torch! And we coulda...goin' on a year now and I ain't had nothin' twixt my nethers weren't run on batteries!"
Mal: (horrified) "Oh God! I can't know that!"
Jayne: "I could stand to hear more."
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Mal: "Zoe, ship is yours. Remember: if anything happens to me, if you don't hear from me within the hour, you take the ship -- and you come and you rescue me."
Zoe: "What? Risk my ship?"
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Operative: "That girl will rain destruction down on you and your ship. She is an albatross, Captain."
Mal: "Way I remember it, albatross was a ship's good luck, 'til some idiot killed it." (to Inara) "Yes, I've read a poem, try not to faint."
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Mal: "I never credited the Alliance with an overabundance of brains, and if you're the best they've got-"
Operative: "Captain Reynolds, I should tell you, so that you don't waste your time: you can't make me angry."
Inara: "Please. Spend an hour with him."
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Book: "I killed the ship that...killed us. It's not very Christian of me."
Mal: "You did what's right."
Book: "Coming from you that means...almost nothing."
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Mal: "So no more runnin'. I aim to misbehave."
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Jayne: "Shepherd Book used to tell me, 'Can't do somethin' smart, do somethin' right'."
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Simon: "My one regret in all of this, is never being with you."
Kaylee: "With me? You mean to say...sex?"
Simon: "I mean to say."
Kaylee: "Hell with this...I'm gonna live!"
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Operative: "Do you really believe that?"
Mal: "I do."
Operative: "You willing to die for that belief?"
Mal: "I am." (pulls out his gun and shoots at the Operative repeatedly) "Course, that ain't exactly Plan A."
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Operative: "Do you know what your sin is?"
Mal: "Aw hell. I'm a fan of all seven."
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And there is the ending:
Mal: "Ain't all buttons and charts, little albatross. Know what the first rule of flying is? Well I s'pose you do, since you already know what I'm 'bout to say."
River: "I do. But I like to hear you say it."
Mal: "Love. Can know all the math in the 'verse but take a boat in the air that you don't love? She'll shake you off just as sure as a turn in the worlds. Love keeps her in the air when she oughtta fall down...tell you she's hurtin' 'fore she keens...makes her a home."