HUGE SPOILERS FOR TDK! But if you haven't seen Dark Knight yet, you probably don't even know what a Batman is and got here by mistake, so we shouldn't have any problems.
1. What are we meant to assume happens once the smoke grenade in the bank manager's mouth goes off? Will he die of asphyxiation? Will all the hostages die from some sort of toxin in the smoke? Is it just a hilarious non-lethal Joker gag? Let's scratch that last one off the list.
2. Despite the fact that the Joker is characterized in this movie as a knife-aficionado, he uses a huge variety of weapons, and only uses a knife about three times. His arsenal includes: shotgun, machine gun, rifle, bazooka, lead pipe, poison (by proxy), car bomb (by proxy), high explosives, and most memorably, a nice sharp pencil.
More thoughts and questions after the jump...(the best one is the last one)...
*Also more TDK icon samplers after the jump...click them to link to the creator's page.
3. Harvey is the second DA Rachel Dawes is seen having a relationship with (it's heavily implied in Batman Beyond). Considering she barely seems to know what a RICO case is, one might question what exactly they're keeping her around the office for.
4. At the fundraiser, Harvey asks Alfred if he's known Rachel for her whole life, and he charmingly replies, "Not yet, sir!". Oh Alfred. Just give it a day.
5. As Gnerd contributor Degan first pointed out, after Batman jumps out of the window to save Rachel, the rest of Bruce's guest are pretty much screwed, as they all are still stuck in a penthouse full of recovering thugs and, uh, THE JOKER. Anyone care to guess what happens next to Gotham's high society elite? "As long as I'm hee-rre...I know this KILLER party game." Haw. I suck. Anyone else got a better line? Come on, I know some of you write fanfic.
6. Heath Ledger must have had so many more incredible performances in him. Of course I realized this on my first viewing, but every viewing cuts a little deeper.
7. I didn't see that Joker had an I Believe In Harvey Dent sticker on his nurse's uniform until my third viewing. I'm dumb. But this is an important detail for anyone planning a Nurse Joker Halloween costume. Not that I am.
8. Given the fact that the murder of Bruce's parents is public knowledge, Harvey and Natasha must think him extraordinarily nihilistic to flippantly remark, "I grew up here, and I turned out okay."
9. Batman seems to have forgotten his loophole on villain deaths from the last movie, namely: "I won't kill you, but I don't have to save you". And yet he saves Joker from a high altitude death, thereby sealing the fate of, if DC comics are to be believed, THE ENTIRE WORLD POPULATION SEVERAL TIMES OVER. Maybe Bats was trying to pull a Gwen Stacy finishing move, but didn't count on The Joker's insanity-powered indestructibility.
One short of a proper top ten list...I can only hope some other helpful multi-viewer will help me out with another observation/nitpick/question.