Darik's Boot and Nuke

For when your hard drive absolutely, positively has to get wiped: Darik's Boot and Nuke.

dban is useful not just for when the feds are knocking down the front door of your survivalist compound, it also helps to blast everything on a disk that you don't want anymore and gives you the peace of mind of knowing that when you repurpose the drive, no one is going find your old Flock of Seagulls MP3s.