It is an established law of science that anything containing Batman is made immediately more awesome by Batman's presence alone. Except maybe Batman and Robin, but I think that film will be flummoxing scientists for centuries to come.
Considering the fact that Batman has been gracing the pages of comics for 75 years, while also making multiple appearances on television, movies and video games, it's not surprising that his signature cowl has gone through a few redesigns.
Salvador Anguiano has compiled all of the Dark Knight's headgear into one slick slide show/poster. The variations are shown below. The gray backgrounds are cowls from comics and video games, the yellow from films and the red from television incarnations. Enjoy:
So many Batman Cowls!
Here is the full poster in all it's cowl-tastic glory!