[Unknown Target]

Doom 3 had great PDA voice acting...and of course, Freespace 2!

[Nuclear1]

I just right-click and hit "Save Target As". Works fine for all of them.

As for another game, Starcraft is full of quotable dialogue. Mostly Raynor and Kerrigan, but some other good lines from other characters as well.

[redsniper]

No one's mentioned Metal Gear Solid yet? Sure there may be some sucky voices *cough*Raiden*cough* but they're far outweighed by all the awesome lines from folks like Liquid Snake, The Boss, and Ocelot just to name a few. "You want eternal rest? I got it right here."
EDIT: come to think of it, Beyond Good & Evil has excellent voice acting as well. It's a shame no one's played it though...

[Sandwich]

Pretty much any comment by Patton or Ransom in Hostile Waters

Hell yeah!

And I'm glad SOMEone mentioned AYB...

How about "Dive! Dive! Dive! Hir your burners, pilot!"?

[Flipside]

Patton : I came, I saw, I blew your lungs out past your backbone....look grateful.

Homeworld Cataclysm : Behold! The Mighty Bentusi! There you are, killing our people because we dare to stand in your way! You're worse than the Beast, at least the Beast doesn't pretend to be righteous!

[NGTM-1R]

"DIVE DIVE DIVE HIT YOUR BURNERS PILOT!"

It had to be done. You know it did.

[karajorma]

Patton : I came, I saw, I blew your lungs out past your backbone....look grateful.

That one is Ransoms. Pattons best is "I drive tanks, boy!" whenever you put him in anything that isn't one

[Turnsky]

"it wants feet"  - Oni

[Prophet]

MDK2: "Must grease pelvis, friction is distracting."  - The four armed dog droid thing I forgot its name.

[CP5670]

haha, I remember that. The dog was Max.

[Setekh]

Oh, MDK2! I never finished the boss from that game...

[pyro-manic]

"it wants feet" - Oni

HMMMM!!!

I must dig that out ad play it again one day...

[phatosealpha]

If we're talking actual voice over files, I'll second System Shock 2's "glory" audiolog.  That thing is just creepy.

After that, half of Jolee Bindo or HK-47's lines from Kotor were a hoot.

If we're counting just written dialogue, I've got to nominate pretty much the entirity of planescape:torment.

[Flipside]

Patton : I came, I saw, I blew your lungs out past your backbone....look grateful.

That one is Ransoms. Pattons best is "I drive tanks, boy!" whenever you put him in anything that isn't one

Your right, the Ransom equivalent of that was 'I'm an Aviator, Ay Vee Ay Tor!' If you put him in a ground vehicle

[karajorma]

I quite liked Elroy, the no nonsense black dude but you get him so late that he doesn't make much of an impression.

[pyro-manic]

I really need to find a copy of that game...

[Grey Wolf]

http://en.wikiquote.org/wiki/HK-47

[Admiral LSD]

"Max, you're in a graphic novel!"

"You're in a computer game Max!"



The "Address Unknown" and "Dick Justice" TV shows are pretty cool too.

[Nix]

"You left me there for a year! That was messed up!"
"Ya wanna see my batteries?" - Pal 18
"Not Brebulan, I hate Brebulan...." -Boots
My god,  Anachronox as a whole was hilarious.  Very well done too. 

Now for one that isn't so great...
The bar with the "australian" bartender in the Lucky Money club, in Deus Ex..
The line: "Rhetoric, and you believe it?"  sounded like "Rheeetik - n yuuh belEEEIT?"

Now for the oddball one...
Anything Peter Stormare says in Quake 4.  He's cool as hell in Prison Break, but in Quake 4, my god, nothing really flows well when he speaks!  I do believe he's Swedish though.  I find it halfway hilarious when he's begging for more backup though. 

[ZylonBane]

Thief-- Any line by Garrett. Or Benny.