Here are my favorites, with links.

Fighter: Black mage is always helping people... The problem is that they almost never understand his unique brand of help so they usually end up yelling... or screaming... or burning...
Episode 45


Red Mage: It's a miracle!
Theif: Let's not forget what kind of god would try to protect BM.
Black Mage: An evil miracle is still technically a miracle.
Episode 324


Red Mage: Wait. You murdered your own blind brother?
Black Mage: It would have been cruel to live after what I did to his eyes.
Episode 518


Theif: What'd I do?
Black Mage: You're Theif.
Episode 537


Black Mage: Fighter, get down from there, you know better than to ride crimes against nature.
Fighter: Aww, man. I never get to ride crimes against nature, or hobos, or nuthin'.
Episode 667


Red Mage: Let's just say that there's no part of the nature vs. nurture debate that can't be solved via highly invasive brain surgery.
Episode 679


Red Mage: Reporting for duty!
Theif: I said checking. Cross-checking.
Red Mage: Ah, yes. I see.
Episode 691

since this thread as hit the deadly sixties i wish to ask for a sticky so that it may reamain and grow.

The quote itself is a classic, but the context just rules.

#472:

Fighter: "Sword Chucks, yo."

http://www.nuklearpower.com/daily.php?date=051022
Black Mage: Are you filled with regret that eventually, there won't be more world to burn?
Ordeal: In the back, yeah.
Black Mage: Sounds like my atrocities, all right. Perfectly normal.

Sorry, but I think this is a bit too close to "favourite episode" to warrant a sticky. We don't need to cover every possible facet of 8BT fandom in stickies. ;)