While I am not a "recruiter" I have worked in HR, my boyfriend is a high-level HR person who used to do a lot of recruiting, and at the company I am currently at I do the initial scan of resumes so take this however you want...
We never look at cover letters. Never.
That being said, do not send a resume in the mail without a cover letter. But it just needs the basics, i.e "I saw the ______ position on/in _______. I'm sending my resume as I am interested, please let me know if you are interested in meeting with me. I can be reached at _______. Thank you" Short and simple. I can see your experience on your resume. I don't need to read through it on a cover letter, too.
I have known recruiters who WON'T look at a resume that has a page long cover letter attached.
Same for email. Don't just send a blank one with an attachement. At least say what job your interested in, but keep it SHORT!
Good luck!