Cover letters to recruiters are different than letters to employers and should have:
An address to a specific recruiter (whenever possible).
The Job Title and # if it is in response to a posted advertisement.
Three to six titles of positions for which you are qualified and interested.
Enough skills and achievements to entice the recruiter to want to read your resume (your resume should entice the recruiter to want to speak with you and / or meet with you.)
Your geographic preference (cities, states, regions, countries) and willingness to travel. "I am open to relocation anywhere in the United States and willing to travel extensively for the right position."
Your salary requirement. "My salary requirement is in the range of $80K to $90K, however, I am open to negotiation based on the responsibilities of the position and the total compensation offered."
Most recruiters prefer to receive cover letters and resumes electronically via e-mail as attachments in MS Word format, ASCII files in the body of e-mails or websites, or PDF files. I recommend calling to find out the preferred version or sending all 3 versions. If possible, follow up with a hard copy by snail mail. So few people do this that recruiters often will read them.
One recruiter told me that she receives so many resumes by e-mail on Mondays that she automatically deletes all of them. If you e-mail cover letters and resumes, avoid Mondays and send hard copies as a back up.
You may want to follow up with a phone call to make sure your e-mailed or snail mailed file was received and to make contact with the recruiter.