opening salution for cover letter

i have had the mind worrying problem of what to write for the opening salutation of a letter when the addressee is unknown. i found this link, hope it helps.

http://www.ego4u.com/en/cram-up/writing/business-letter/salutation

If you don't know the person's name:

There are several possibilities to address people that you don't know by name:

salutation	when to use
Dear Sir / Dear Sirs	male addressee (esp. in British English)
Gentlemen	male addressee (esp. in American English)
Dear Madam	female addressee (esp. in British English)
Ladies	female addressee (esp. in American English)
Dear Sir or Madam	gender unknown (esp. in British English)
Ladies and Gentlemen	gender unknown (esp. in American English)
To whom it may concern	gender unknown (esp. in American English)