“Oh what fresh hell is this?”
I actually use this one quite a bit. 
Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and as it always has, rock crushes scissors.
Hey, woman, cool your jets. I gave you my virginity.
One more time. 
Mary Cooper: Leonard, I raised that boy from birth. I’ve seen him at his best, I’ve seen him at his worst. Nothing he could do would surprise me.
Leonard: Hold that thought (Opens door to Sheldon’s room). Surprise!
“Wouldn’t you prefer to socialize with Tom, who is a sexually passive outdoors-man?”
Sheldon: Well, this is confusing for me. But I don’t want to stand in the way of your happiness. So, I will condemn you internally while maintaining an outward appearance of acceptance.
Mary: That is very Christian of you.
Penny seductively removing her horn-rim glasses:
“Molecules…”
I brought your whiskey, Meemaw. Just the way you like it. Lots of it, in a glass.
Surely. Scissors cuts paper, paper covers rock, rock…
Wolowitz: I have a Master’s degree!
Gablehauser: Who doesn’t?
“Crap on a cracker!”
Oh, beef, how I shall miss you.
I love the “Penny slips in the shower” episode.So many great lines in that one, as many of you have quoted.
My favorite character in the show is Zak. I wish they would use him more.
Zack: I just think splitting up can be rough on kids.
Penny: We don’t have any kids.
Zack: Are you sure? 'cause you didn’t know we were married until this morning.
Oh menopause, nature’s birth control.
The hero always peeks.
I paraphrase:
Penny:“Leonard’s great! He’s smart, he’s sweet and in the bedroom? Hoo boy - let me tell you, he … really tries.”
Amy (on being handed an eyelash curler): “It looks like something Tinkerbell’s gynaecologist would use.”
“Happy wife, happy life. Let’s eat!”