What not to say in an interview.
Here is a cover letter sample to give you some ideas and inspiration for writing your own cover letter.
Expert Advice: 8 Tips for Writing a Standout Cover Letter (I really like this one)
Here's an infographic that points out very clearly the content elements of a good cover letter.
The 13 Best-Kept Cover Letter Secrets. This has to be the best cover letter advice out there.