Per Scholas addresses the security concerns of corporations, institutions, and government agencies by adhering to a rigorous data-wiping protocol that meets the standards of the Department of Defense, banks, and other financial institutions.
If you prefer to sanitize your disk drive yourself, I present Darik's Boot and Nuke, a self-contained boot floppy that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect. http://dban.sourceforge.net/