You might not consider this a direct answer, but as someone who has successfully landed no less than 12 increasingly great positions in my career, I have to say that I have never written a cover letter. I also have never submitted a blind application with resume. I have found all of my positions through networking. I use my friends, family, old co-workers, and these days services like LinkedIn where I cultivate a network of relevant and well thought of associates.
I think that if you depending on a cover letter or resume to get you a job, you might be overlooking some of the vital elements of job searching. I have written a couple of hubs on this topic, which I won't shamelessly link to this answer, but I would recommend that you read them if you have time. I hope this is helpful to you.