Newbie here from the UK *waves*. Just finished watching season five and felt like Cas stole the character with the best lines award from Dean.
Here's a small sample of my faves:
Raphael: I will find you,
Cas: I know but for today, you're my little bitch.
Sam: (on seeing a beated up Dean) What the hell happened to him?
Dean: Did he just say "On a bender"?
Cas: That information is not relevant. (just love how he dismisses it like a typical drunk lol).