<wandering slightly off topic> If you're writing to clients or potential clients,and there aren't to many of them, it's probably worth ringing the company and getting the correct name, business title and salutation.
I'd avoid "Dear Sir or Madam" or "To Whom it May Concern", to me, it screams mass mailing, and goes straight in the bin. "Dear Felllow Professional" or the like are only slightly better. </wandering slightly off topic>
Rosie
"Never express yourself more clearly than you think" (Niels Bohr)