Wolowitz: So, what are we watching? Sex in the City, yikes!
Penny: Hey, I happen to love this movie.
Wolowitz: Fine, let's watch it. Maybe all our periods will synchronize

Sheldon: Yes, since their relationship became carnal, Penny has updated his designated term of endearment, distinguishing him from those she calls "sweetie," usually as an attempt to soften a thinly-veiled insult.
Penny: You're boring people, sweetie.
Sheldon: Although sometimes, she omits the veil entirely.

Penny: I give up, he's impossible
Sheldon: I can't be impossible, I exist. I believe what you meant to say is, "I give up, he's improbable."

Penny: I'll tell you what, next french toast day, I'll make you oatmeal
Sheldon: Good lord, are you still gonna be here next french toast day?

Oh man, did the KISS Army repeal "Don't Ask, Don't Tell?"

Penny [after seeing Wolowitz in his goth outfit]

Leonard: Why would you buy peppermint schnapps?
Penny: Because I like peppermint, and it's fun to say schnapps!

Penny: You know, I do understand what you're going through.
Sheldon: Really? Did you just have the Nobel Prize in Waitressing stolen from you?

Leonard [about snuggie gift]: what does this mean?
Penny: Wine, credit cards and late night television are a bad combination

Penny [to comic book store owner]: What would you recommend as a gift for a 13 year old boy?
Stuart: A thirteen year old girl

Penny [at comic book store]: Everyone's staring at me!
Leonard: Don't worry, they're more scared of you than you are of them
Penny: Unlikely

Wolowitz: According to Alicia's Facebook page, she's hooking up with one of the producers on CSI.
Penny: Dead whore on TV, live one in real life.

Penny: It looks like the MySpace page of a 13 year old girl
Leonard: No it doesn't
Wolowitz: Oh please, Dateline could use it to attract predators

TBBT Quotes

It's very simple. 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

Sheldon

Leonard: Hi. I'm Leonard. You are beautiful. You pop, sparkle and buzz electric. I'm going to pick you up at eight, show you a night you will never forget.
Raj: Where are we going?