Leonard: Oh, I know. This might help. *Gets a ring out of his wallet*
Penny: Where did you get a ring?
Leonard: I've had it for a couple of years. Not important. Penny, will you marry me?
Penny: Oh, my God, yes.
Leonard: This would have been so much more romantic if you didn't have monkey hair on your finger.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Bernadette: Maybe we should get one of those machines to help her up the stairs.
Howard: You mean a forklift?

Bernadette: I'm glad I got that mocha. And you know what else I'm glad about? I bought you a brownie and I ate it in the car!

Penny: I finally realize I don't need to be famous or have some big career to be happy.
Leonard: Well what do you need?
Penny: You, you stupid Poptart.