Many people underestimate the importance of a cover letter. Your cover letter is an opportunity to introduce yourself, showcase your writing abilities, convey your feelings and attitude toward the position, and expand on your strengths and goals. It should complement your resume, not regurgitate it. Take a look at the Slides presentation about what to include in your cover letter and review the samples. You'll see the difference between a well-written cover letter and a poorly written one. A well-written cover letter can set you apart (and above) from other candidates!
Look here to see a helpful presentation on creating cover letters!