playing all these good old games makes me reminisce about awesome gaming moments
here's one i just saw in abe's oddysee:
"work hard, die young, win valuable prizes!"

I remember that! It has been a while since I busted that out...

"I invited your best friend the Companion Cube, but he couldn't come because you murdered him."
Guybrush: How much wood would a woodchuck chuck if a woodchuck could chuck wood?
Carpenter: A woodchuck would chuck no amount of wood since a woodchuck can’t chuck wood.
Guybrush: But if a woodchuck could chuck and would chuck some amount of wood, what amount of wood would a woodchuck chuck?
Carpenter: Even if a woodchuck could chuck wood and even if a woodchuck would chuck wood, should a woodchuck chuck wood?
Guybrush: A woodchuck should chuck wood if a woodchuck could chuck wood, as long as a woodchuck would chuck wood.
Carpenter: Oh shut up.

"Revan was power. It was like staring into the heart of the Force. Even then, you could see the Jedi he would slay etched on his soul." ―Kreia
Revan rules.

Bob Page: "Soon, I will become pure energy. I will burn like the brightest star."
JC Denton: "You're gonna burn, all right."
The line always makes me smile.

Best as in "Best Bad" or "Best Good"? If you're talking about the former, every line in Resident Evil 1 wins.
"Jill...here's a lockpick. It might come in handy if you, the master of unlocking, take it with you."
"You were almost a Jill sandwich!"
I really can't think of a good example for the latter.

oh yeah.
Anything said by main character in VtM: Bloodlines when playing a malkavian. Every single sentence is simply priceless.

"She has a tendency of.... Exploding!" - The villain character in Pariah. I've never ROF'd at a cut scene that much in my life.
"How about some scat you little twat?" - The Great and Mighty Poo from Conker's Bad Fur Day. How Nintendo ever approved that game is beyond me, but I'm so glad they did.
"Don't Come! Don't Come!" - A Victim in House of the Dead 2. Engrish has never been so amusing.
"It's a rubber ducky." - April Ryan in The Longest Journey. For some reason the way she says it gets me hot under the collar. Then again I've always had a soft spot for her >.> TLJ has so many amusing but also profound quotes, its a goldmine.
"..." - Gordon Freeman.
I'll go dig up some more.

The Jill sandwich quote gets me every time... hilarious stuff.
Anyways, there's a ton of Team Fortress 2 quotes that are great:
Heavy:
"WHERE DID WE GO SO WRONG?!?!"
"Look at you tiny-itty-bitty men running from sandwich! It's good time to run cowards!"
Scout:
"Yo! Batter up! Eat it, fatty! Oh yeah! You are real scary!"
There's a ton more and they're all hilarious...

My favourite was probably the russian mobsters when you convinced the boss he was a hungry bear and his two offsiders were tasty salmon.
That or jeanette commenting how nuts you are, you know you've got to be pretty bad when SHE comments on it...

portal has some gems:
“Didn’t we have some fun though? Remember when the platform was sliding into the fire pit and I said ‘Goodbye’ and you were like ‘NO WAY!’ and then I was all ‘We pretended we were going to murder you’? That was great."
and of course "the cake is a lie"

"Conscience? You dare speak to me of conscience. Only when you have felt the true gravity of choice, should you dare question my judgement. Your life span, is a flicker, compared to the mass of doubt and regret that I had borne since Mortanius first turned me from the light. To know the fate of the world hangs dependant on my every deed, can you even begin to see what action you would take in my position."
"Raziel. Redeemer and destroyer. Pawn and messiah. Welcome time spanned soul. Welcome to your destiny"
"But does on ever truly have a choice? One can only match, move by move, the machinations of fate. And thus defy the tyrannous stars."
"Alas poor Nupraptor i knew him well...well not really"
(After kain appears)
Raziel: "oh no, everytime you show up something monumental and terrible happens, i dont think i have the stomach for it"
"You should never have betrayed me. You could have been my queen. Now, you have left me alone."
Just so many quality lines in the legacy of kain series these are just a few. I reckon its got to be just about the best written game ever made in my humble opinion.

There's tons of good ones from Portal:
"Speedy things goes, speedy thing goes out."
"If at first you don't succeed, you fail" (I think that's followed by "Good luck!")
There's a guy in Knights of the Old Republic that says "In case you haven't noticed, there's a war going on." It's awesome to me because one day it popped in my head as a response to something, but I couldn't remember what movie it was from. After a while I remembered it wasn't from any movie, but from KotOR. The guy says it that awesome, apparently.
In the new zombie mode of Call of Duty: World at War, when you pick up a shotgun sometimes your guy will say "This is my boom stick!"

pretty much everything this guy says
-The Enrichment Centre regrets to inform you that this next test is impossible. Make no attempt to solve it.
-Fantastic. You remained resolute and resourceful in an atmosphere of extreme pessimism