Xander: "I resent that!"
        Giles: "..."
        Xander: "Or possibly thank you."

Xander: "Can I just say, 'Gyughhh!!!'?"
              Buffy: "I see your 'Gyughhh' and raise you a 'Nyaghhh!!!'"
Surprise/Innocence
Xander: "I mean, what kind of a future would she have really had with him?
         She's got two jobs: Denny's waitress by day, Slayer by night. And Angel's
         always in front of the TV with a big blood belly. And he's dreaming of the glory
         days when Buffy still thought this whole creature of the night routine was a big
         turn-on."
         Willow: "You've thought way too much about this."
         Xander: "No, no, that's just the beginning. Have I told you the part where I fly
         into town in my private jet and take Buffy out for prime rib?"
         Willow: "Xander."
         Xander: "And she cries?"

Cordelia: "I know, you were too busy rushing off to die for your beloved Buffy.
           You'd never die for me."
           Xander: "No, I might die from you. Does that get me any points?"
           Cordelia: "No."
           Xander: "Come on, can't we just kiss and make up?"
           Cordelia: "I don't wanna' make up. But I'm okay with the other part."

Xander: "Whoa, whoa! I...I think I'm having a thought. Yeah, yeah, that's a
         thought. Now I'm having a plan."

Xander: "Just meet me at Willow's house in half an hour and wear something
         trashy...er."

Cordelia: "Well, does looking at guns make you wanna' have sex?"
              Xander: "I'm seventeen. Looking at linoleum makes me wanna' have sex."
Phases
 
Willow: "Great, I'll give Xander a call. What's his number? Oh yeah,
              1-800-IM-DATING-A-SKANKY-HO." (about Xander)

Larry: "I'm gay. I...am gay."
       Xander: "I heard you the first time."
More coming soon!