well, it depends what kind of job it's for.
i do a lot of reviews of resumes and stuff here for new hires so maybe i can help?
generally, a good cover letter would say something like 'i am enclosing my resume as application for the position of BLANK'. and then you know, BRIEFLY list your experience or skills that will make them want to bother reading your resume. don't get wordy though.
put your phone number at the top of it, so they dont have to search for it. then say something like 'if you would like to schedule an interview with me, please call/email me at the number above'. and so on.