(No sarcastic thank you included)
Castiel: Then the most fearsome wrath of heaven would rain down on that demon. Just so you understand… why I can’t help.
Dean: Thanks, Cas.
5x04 (it really counts as a thank you):
Dean: That’s pretty nice timing, Cas.
Castiel: We had an appointment.
Dean: Don’t ever change.
5x16 (I don’t think this one is sarcastic, he just used a pop culture reference):
Castiel: (on TV) Don’t go into the light.
Dean: Okay. Thanks, Carol Ann. What was it?
Castiel: About your brother. I… I don’t know what’s wrong with him, but I do want to help. I’ll make inquiries.
Dean: Yeah. Thanks.
Dean: Thanks, Cas. Hadn’t it been for you –
Castiel: Crowley was right. It’s not going well for me upstairs.
Dean: If there’s anything we can do –
Castiel: There isn’t. I wish circumstances were different. Much of the time I’d rather be here.
Dean: Look, Cas, we know you got a steaming pile on your plate. There’s no need for apologies. We’re your friends.
Dean: It is good to see you, Cas.
Castiel: You all right?
Sam: Yeah. Perfect timing, Cas.
Castiel: I’m glad I found you. I come with news.
Dean: Yeah? What?
Castiel: I firmly believe Crowley is alive.
Dean: Yeah. You think, Kojak? Well, Bobby, what do we think about Cas saving our asses…Again?
Bobby: I think we owe you an apology.
Sam: We’ve been hunting Crowley this whole time…And keeping it from you.
Bobby: We thought…You were working with him.
Castiel: You thought what?
Dean: I know. It’s crazy, right?
Bobby: It’s just that you torched the wrong bones. It doesn’t matter. We - we were wrong.
Castiel: You know…You could’ve just asked me.
Dean: And we should have. We never should’ve doubted you. It’s…I just hope you can forgive us.
Castiel: Wonders never cease. They trusted me again. But it was just another lie. It’s forgotten.
Castiel: She’s fine now. She’ll wake soon. Dean, I said I’m sorry and I meant it.
Dean: Thank you. I wish this changed anything.
Castiel: So, none of this should cause you any ill effect. I went to a little farm in Normandy for the wheat and the lettuce and tomato and – and I thoroughly examined and comforted the pig before I… slaughtered it for the ham. Here. You need your strength.
Dean: Thanks, Cas.
Dean: Thanks for the lift.
Castiel: My pleasure.
Castiel: Well, I’ll go with you. And I’ll do my best.