As you are all aware by now, you must consider the constructed nature of the film when writing your essay.
Here are some links that might provide a last minute surge of inpiration.
http://vcewaterfrontcharacters.wordpress.com/ – This blog has pages on characters, themes, metalanguage and setting.
http://education.theage.com.au/cmspage.php?intid=136&intversion=252 – Roger Stitson explores the way Kazan uses the costumes and images of the characters to convey his ideas.
http://www.studymode.com/essays/Cinematic-Techniques-In-On-The-Waterfront-994300.html – This is the introduction and first paragraph of an essay for sale. I think it provides some nice clues on how to write about the film. I’m not suggesting you buy it.
OTW+film+techs – A powerpoint presentation that explores some film techniques and examples.
http://www.cios.org/EJCPUBLIC/005/1/00513.HTML – Something more sophisticated for those looking for that little bit more that you know you know, but just can’t put your finger on it.