Securely Wiping Disks With DBAN - Boot and Nuke!
DBAN (Darik’s Boot And Nuke) is designed to fully and securely wipe your disk. It’s a downloadable self-contained boot disk, available for CD/DVD, floppy disk, or USB flash drive. Boot from it, and it will look for hard disks on the system, then give you the option of deleting any or all of them. (Note that for RAID arrays you may need to disassemble the array first.)
via LinuxPlanet - Tips - Securely Wiping Disks With DBAN - Boot and Nuke!.