Sometimes in all the advice for jobseekers, we miss one important ingredient for your cover letter.  In my mind, there is one thing that trumps all else:

Do not use a ‘standard’ cover letter.  Find out something about the company to which you are applying, and make your cover letter stand out by referencing THIS company, an issue or, even better, a specific quality or thing you can bring to THIS job and to THIS company.

Here is an example:

“I was reading about your chairman’s message on your website and was interested in the new division that was created last year.  In my resume, you will see that I have some experience in helping with the inter-company communications issues raised when a company creates a new division.”

Specificity sells.