Ledger's performance of the Joker was punctuated by his tragic death shortly after shooting ended. It was said that he had trouble sleeping because of the strain of his performance. Climbing into the Joker's head couldn't have been a pleasant experience, which may have contributed to the accidental drug overdose that killed him. (Source.)

The Motion Picture Academy usually turns its nose up at superhero movies—they're kind of snobby snobs—but they couldn't say no to Ledger's performance here. He posthumously won the Best Supporting Actor Oscar in 2009. Check out Kevin Kline gushing all over his performance. (Source.)

At one point, Bruce Wayne goes out in a Lamborghini to stop the Joker's death threats from taking out an innocent man. The model he's driving is called a Murcielago, which happens to be the Spanish word for bat. (Source.)

Christopher Nolan notoriously hates using computer-generated effects. The more real he can get, the better. So at the end of the big chase, when Batman uses his Bat-pod to flip the 18-wheeler? They actually flipped an 18-wheeler. Hydraulic cannons were fired from the bottom of the truck, causing the whole kit and caboodle to do a great big flip. (Source.)

Gordon's young son James Jr. plays a small role in the film, but if you look carefully, you'll see another child among his brood: a little red-headed girl. They don't go into her at all, but if you read the comics, you know who she is: Barbara Gordon, who will one day grow up to be Batgirl. For our money, she should have been the one calling after Batman at the end, but Nolan thought the character was too close to the campy '60s version of Bats, so poor Barbara got left on the sidelines. Big mistake Chris. (Source.)

That old man at the party who tells the Joker that they're not afraid of him? That's Senator Patrick Leahy, from the great state of Vermont. He's a big Batman fan and previously appeared in Batman & Robin (we're guessing he regrets that one) and Batman: The Animated Series. (Source.)

During the interrogation of the Joker, ole Whiteface tells Batman that "you complete me." That's a reference to Tom Cruise's famous line in Jerry Maguire. It's also a likely dig at Cruise, whose romance with Katie Holmes broke while the pair were on tour to promote Batman Begins. Nolan felt that the TomKat show upstaged his movie, and included a little zinger in the sequel to get even. (Source.)

Okay, time to get really deep here. Remember the video of the Joker torturing the Batman wannabe?
If you look close you can see the poor faux bat framed in front of a huge side of meat. Believe it or not, that shot is a very subtle reference to a painting called Figure with Meat by Francis Bacon. In Tim Burton's Batman, the Jack Nicholson version of the Joker spares it in his rampage of the museum.
Oh yeah, and the painting is located at the Art Institute of Chicago… the same city that stands in for Gotham City in The Dark Knight. Minds blown yet? (Source.)