Military personnel locators now require that requests for information be submitted in writing and may have a nominal fee. The best site we've found for providing the information for each service is from about.com, linked below. It has very thorough information about how to locate current or former members of the U.S. military by branch of service.
We also subscribe to FedSearch Suite published by Carroll Publishing. Within this database, you can look up a service member by their name (first or last) and title or department. NOTE: this database is best for searching high ranking / department level personnel. ONLY AVAILABLE TO NPS PERSONNEL.