The following quotes are all from Season 3. Why do you start with season 3 you might ask. Well, those are the episodes I'm currently watching, and since I don't have an eidetic memory like Sheldon does - I can't quite remember the best stuff from the first two seasons.
Penny and Leonard have just - finally - started sleeping together. One morning Leonard catches Penny dancing in the kitchen making French toast. On oatmeal day! Sheldon cannot live with this, which, on her turn, Penny can't seem to deal with:
Penny: You know what, 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"
A bit later Sheldon smells a plate of French toast:
Sheldon: "That does smell nice. Too bad it's monday"
And throws the four slices in the trashcan.
Sheldon: "Interesting, sex works even better than chocolate to modify [human] behaviour. I wonder of anybody else has stumbled onto that?"
Sheldon: "This movie baffles me every time we watch it"
Leonard: "What do you mean?"
Sheldon: "Well, the instructions are very clear. Don't feed the gremlins after midnight, don't get the gremlins wet. How hard is that?!"
Howard: "Ok, this time you don't have to eat the tur-brisk-gefilte"
Raj: leaves the room
Howard: "I don't even chew it. I swallow it like pibbles."
Howard: "So what are we watching? Sex and the City, yikes!"
Penny: "Hey, I happen to love this movie"
Howard: "Fine, let's watch it. Maybe all our periods will synchronise"
Leonard: "Alright, we're gonna be designing an experiment to look for the inhialiation spectrum resulting from dark matter collisions in space"
Raj: "Oeoe, dark matter. We'd better bring a flash light"
Raj: "My God. You think that every thought that comes out of your mind is pure gold. Well, I'll tell you. Some of your thoughts are pure kaka"
Raj: "It means doo doo."
Raj: "So that's how it works. I have a teenie bladder, and now I don't get a hot girlfriend?"
Howard: "Yeah, Raj - that's how it works"
Penny (in bed): "Owwww. You are a genius!"
Howard (same bed): "Not really, I googled how to do that"
Penny: "The great thing about Ernie was that he never asked for anything. He just gave"
Howard's date: "I couldn't ride a a bicycle because my mother was worried that I would hit a bumb and lose my virginity."
Howard; "Ow whow, you didn't - did you?"
Date: "Not on a bicycle. In a Camery"
Howard: "Whow, Corola!" (pointing at himself)