My favourite was from Extras when Andy Millman was talking to Ben Stiller:
BEN: And who are you?
ANDY: Nobody.
BEN: What?
ANDY: Nobody.
BEN: Exactly. And who am I?
ANDY: Either Starsky or Hutch, I can never remember.
BEN: Was that supposed to be funny?
ANDY: You tell me, you were in it.
Oh god yes. I love that scene.
There are so many great lines to choose from!
Not exactly a line, and I cant repeat it exactly but:
series one, where Brent is saying to the workers, 'you're not getting fired, you're not getting fired, (looks at someone, pauses, then moves on), you're not getting fired'
creases me up.
Quote: manchester's trendy chorlton @ May 6 2008, 4:04 PM BSTNot exactly a line, and I cant repeat it exactly but:
series one, where Brent is saying to the workers, 'you're not getting fired, you're not getting fired, (looks at someone, pauses, then moves on), you're not getting fired'
creases me up.
That was literally the first moment I saw the Office. Can't remember if it was during the original run or the repeats but I stumbled across it while flicking through the channels rather than have it recommended to me.
What was your immediate response?
‘If you want the rainbow, you’ve gotta put up with the rain.’ Do you know which philosopher said that? Dolly Parton. And people say she’s just a big pair of tits.”
"Yeah, it's a mix of flash dance with some MC hammer shit"
Quote: manchester's trendy chorlton @ May 6 2008, 4:18 PM BSTWhat was your immediate response?
I thought it was a real documentary but after a few minutes I had my doubts - it was too bizarre to be true.
In the opening episode of The Office when he is introducing the staff in his office BENT: Lovely Dawn Tilsey, are receptionist. I would say at one time or another everyone in this office has woken up at the crack of Dawn.
Classic Gervais one liner.
Oh yes!
That's a brilliant line.
Quote: Jack Massey @ May 6 2008, 9:45 PM BSTIn the opening episode of The Office when he is introducing the staff in his office BENT: Lovely Dawn Tilsey, are receptionist. I would say at one time or another everyone in this office has woken up at the crack of Dawn.
Classic Gervais one liner.
Yes but not original. That particular 'one liner' is old enough to have been in music hall.
By 'best', I assume the OP meant 'least bad'...
I do that all the time in all honesty. But who doesn't?
Can't remember it exactly, but from The Office, it was something along the lines of, "We're a family, Niel isn't going to come in a fiddle with it, if anyone is going to fiddle with my kids it will be me".
Quote: Griff @ May 6 2008, 9:51 PM BSTThe line that made my jaw drop is when Brent is role-playing with the trainer a scenario about bad service in a hotel, and shouts "There's been a rape up there!" in order to "win" the exchange.
Yes, I love that too. He follows it up by saying in that understated way of his: "Get their attention."
Sure got mine! 
A line I never heard before until recently that made me laugh out loud was during the jelly incident when Brent appears and says “Slow down, you’re moving too fast...Solomon’s here.” Then gives the camera a little wink