Benefit of a Cover Letter

I remember a time when I sent my CV to a big company. It was a company which assembles generators, reactors with steel tubes/pipes, etc. for use in Nuclear Plants. It was surprising to me that nobody answered. I called the Human Resources Department and asked why they didn't invite me for an interview. The clerk explained that they received two thousand CV's and my number was 777. He really tried to read them all but it wasn't possible due to the large number received. I informed him that I'm very suitable for this position and eventually they invited me for the meeting.

The purpose of Cover Letter is similar: to deliver CV to the employer. Obviously, it is very important to not recite your CV but to bring to the attention of the person to your CV.

This is an example of a formal introduction:
I am writing to enquire if you have any vacancies in your company. I enclose my CV for your information.
This is my suggestion of a possible beginning of the letter with less formal phrases:
I'm writing to you to ask about possible vacancies in your company. My CV is attached in this letter.

It would be not a bad idea to write the cover letter to yourself, incorporate in it your own hobbies (The Internet, technologies, Linux, foreign languages, etc) as an additional advantage.