4. The Flaming Bat
Some might think this one the most contentious Easter Egg on the list, but it's still surprisingly compelling. In The Dark Knight when Batman saves Harvey Dent from a grizzly, hot death, and Rachel dies at the second location, the flame that engulfs his face and transforms him into the monster we later see seeking vengeance for his girlfriend's death bears an uncanny resemblance to the flaming Batman logo that played such a key part of the film's poster. Maybe that's pushing it, but the SFX department clearly consciously choose that flame configuration, and it's nice to think they hid the reference in there.