From HL1:
G-Man: Gordon Freeman, in the flesh. Or rather, in the hazard suit. I took the liberty of relieving you of your weapons; most of them were government property. As for the suit, I think you've earned it. The borderworld, Xen, is under our control for the time being, thanks to you. Quite a nasty piece of work you managed back there; I am impressed. That's why I'm here: I have recommended your services to my... employers, and they have authorized me to offer you a job. They agree you have limitless potential. You've proved yourself to be a decisive man, so I don't expect you'll have any problem deciding what to do. If you're interested, just step into the portal and I'll take that as a yes. Otherwise, well, I can offer you a battle you have no chance of winning. Rather an anti-climax after what you've just survived.
Nihilanth: You are man... he is not man... for you he waits... for you...
Nihilanth: The truth... you can never know the truth... you can...
From HL2:
Barney: Hey Gordon! If you see Dr Breen in there, tell him I said [crashing noise] you!
G-Man: Rise and shine, Mr Freeman. Rise and shine. Not that I wish to imply you have been sleeping on the job; no one is more deserving of a rest, and all the effort in the world would have gone to waste, until... well, let's say your hour has come again. The right man in the wrong place can make all the difference in the world. So, wake up, Mr Freeman; wake up and... smell the ashes.
Dr Kleiner: Alyx has just installed the final piece of our resurrected teleport.
Barney: You mean it's working? For real this time? Because I still have nightmares about that cat.
Alyx: What cat?
Alyx: Come on Gordon! We may still have...
[explosion; time suddenly freezes and G-Man appears]
G-Man: Time, Dr Freeman? Is it really that time again? You've accomplished much in a small timespan. You've done so well, in fact, that I've received some interesting offers for your services. Ordinarily, I wouldn't contemplate them, but these are extraordinary times. I do apologize for what must seem an abitrary imposition to you. I trust it will all make sense in the course of.... well, I'm really not at liberty to say. In the meantime... this is where I get off.
[G-Man walks through a bright white portal which shuts behind him, leaving Gordon in suspended animation]
Vortigaunt: Our greatest poet describes it thus: gallum galla gilla ma.