One of my most favorite ones is when they were discussing about the auction they had to go to and if they had anything to put for auction. Sam only looks at Dean's car.
Don't even think about it. If you say it, I'm gonna kill you, your children, and your grandchildren.
And a favorite serious one:
Killing that guy, killing Meg. I didn't hesitate, I didn't even flinch. For you or Dad, the things I'm willing to do or kill just scares me sometimes.
I also loved Ellen's line:
They say you can't protect your family forever. Well I say screw that. What the hell's family for?
More awesome ones:
Dean: Damn cops.
Sam: They were just doing their job.
Dean: No, they were doing our job, only they don't know it so they suck at it.
(about Bela) You know what? Your right. I'm not going to kill her. I think slow torture's the way to go.
Sam: "He's famous, kind of."
Dean: "For what, douchebaggery?"
I like him. He says okie dokie.
I miss conversations that didn't start with 'this killer truck.
What do I look like, Dr Angel, Medicine Woman?
You go with Efron. I've got Bieber.
No, we were talking about our feelings, then we started talking about our favourite boy bands. Of course we were talking about a case!
Sam: Kids are the best?
Dean: Yeah, I love kids.
Sam: Name three children that you even know.
*Dean thinks hard and Sam turns around to walk away*
Dean: I'm thinking!
Dean: Ya know she could be faking.
Sam: Yeah, what do you wanna do, poke her with a stick? *Dean considers this seriously*
Sam: Dude, you're not gonna poke her with a stick!
I'm kind of the black sheep of the family. Handsome though.
It's like we got a contract on us. You think it's 'cause we're so awesome? I think it's 'cause it's we're so awesome.
Actually, we are... uh, teddy-bear doctors.
Dean describing Sam: Dean, this is a very serious investigation. We don't have any time for any of your blah blah blah blah.
Come here. I'm gonna lay my head gently on your shoulder. Maybe we can cry, hug, maybe even slow dance.
Jo (handing Dean a file): Take it. It won't bite.
Dean: No, but your mom might.