Another Mesh quote I love:
Mossman: The zero point energy field manipulator is *not* a toy, Alyx.
Alyx: Ugh, let's just get out of here.
Mesh: Yea it is! I wanna use it as a toy! You have no idea! Seriously, look at me! Yeah, that's right. With your eyes. Come on. (Judith looks) That's...
The Mesh-vid with Eli's lab comes to mind.
Alyx: She's one of the reasons I spend so much time outdoors
Mesh: Ugh, can't blame ya.
:D
Or when a zombie crashes through a door in Ravenholm:
Mesh: OHHHMYGOOOOOD!!!!
:D
The best line in HL2 (which happens to have swearing in it) was Barney's line:
I got such a great feeling of satisfaction when I heard him say that. :)