There are a lot of scenes from TDK that I really loved and it's very hard to choose just one. In terms of Joker scenes, the first that comes to mind is practically his first, right before leaving the bank:'I believe whatever doesn't kill you simply makes you...stranger'. I just love the delivery of that line. Another one that obviously comes to mind is his last...I just love Joker's lines there about the nature of his and Batman's conflict('This is what happens when an unstoppable force meets an immovable object'). Another thing I really like about that scene is that Joker practically defines Batman when he says 'You truly are incorruptible, aren't you?'.
Batman's first appearance in the movie was another scene I really liked. What I enjoyed about it especially, was the feeling the mobsters were having when the real Batman arrived, something along the lines of 'oh ****, things just go serious'. The exchange he had with Scarecrow and the fake Batmen('I don't need help!, Not my diagnosis.') was nice as well. And I loved the 'I'm not wearing hockey pads line'. I like that he was practically telling them...dudes, I've got a tank and a goddamn battle suit, what more do you need? The scene with Batman 'interrogating' Maroni was cool as well...Bale was just so intense in that scene.
And of course the final scene was great as well...right from the beginning, when Gordon arrives to confront Harvey. I loved Harvey's line 'It's not about what I want, it's about what's FAIR!'. But the highlight of that entire sequence are Batman's lines at the end, as well as Bale's delivery. I really liked the subtle appearance of Bruce's voice, when Batman delivers his final lines in the film. Epic!