Look. I know you want a job. You need to tell me a) why you want this job, b) why you are the best possible candidate for this job, and c) how your entire life up to this point has been preparation for kicking the ass of this particular job. If you send a "Dear Sir" (or, worse, a "Dear Sir or Madam") cover letter with some generic info i could get from your resume, there is absolutely no chance that you will be hired. Why waste both our time?