Great Cover Letter
Taking your good cover letter and turning it into a great cover letter requires some careful focus. Read over the position you are applying for closely, and try to make a list of all the skills that you feel would be important for that position. Then, try and make a list of your own that highlights the different work experience you have had that would show your success at having those skills.
Then, when writing your cover letter, try and highlight on these different experiences. All of them should already be on your resume, so bringing those details into your cover letter shouldn't be that difficult. Mention your best experiences and a few of the details that really matter about those positions. These experiences will really help you have a great cover letter.
Lastly, to make sure you have a great cover letter, send it as the body of an email, rather than as an attachment. In this day and age of viruses, many companies will be reluctant to open a cover letter that is sent as an attachment. If worst comes to worst, you can always do both, sending your cover letter as an attachment, and as the body of an email. Following this advice, you should be well on your way to a great cover letter.