Last time I applied to jobs, and got calls from recruiters, I asked what stood out. It was always the resume. I asked if the cover letter helped. Response was usually "You submitted a cover letter? Let me check. Oh hey, I see you submitted one."
My advice is the opposite of another comment: Write one only if you have a "direct pass" that avoids the HR/recruiter filter. Recruiters don't seem to look at them, and HR folks usually don't know enough about the job to value them.
This is a good comment, but see my other post in this thread - at least with me, the cover letter itself gives you a "direct pass" for one of my vacancies. That's not advertised in the posting or anything, but I'm betting I'm not entirely unique in doing that.
At the very least, a cover letter can't hurt, so write one for a position you're really interested in!
My advice is the opposite of another comment: Write one only if you have a "direct pass" that avoids the HR/recruiter filter. Recruiters don't seem to look at them, and HR folks usually don't know enough about the job to value them.