I have never bothered completing a cover letter with a submission, and I personally believe that a cover letter violates the essence of blind review. The work should stand on its own. What might a cover letter accomplish? Would it persuade an editor to send a submission to reviewers more likely to endorse your paper or bias the editor's perception of your work in some other manner? My suggestion is to simply submit your work. Who you are, who you know, and other work you have done should not influence the editorial review process.