I’m an avid reader of lifehacker.com and I recently read an excellent article on permanently deleting data and the tools to do so. Deleting data alone does not remove the information from your hard drive, it only removes the “pointer” to the information. To securely delete data, you have only a few options… wipe/erase, put an industrial magnet to your hard drive, or physically DESTROY it…

Here are some of the tools they mentioned to securely wipe data from your system:

Total Disk Wipe - All Platforms

Darik’s Boot and Nuke - an open-source boot disk utility (read: works on nearly any computer) that supports a wide variety of disk wiping methods and operates from inside the computer’s RAM, allowing it to scrub the disk thoroughly at a remove.

Selective File Wipe - Windows

DeleteOnClick - Integrates with the Windows shell, adding a “Securely Delete” option to the right click menu which engages a Department of Defense 5220.22-M overwrite on the files.

Eraser - In addition to securely deleting individual files, Eraser can be scheduled to perform regular overwrites of empty disc space ensuring you catch those orphan files hanging outside the reach of Windows.

Wipe File - Portable application that overwrites the specific disk space occupied by the file you’d like erased and leaves the rest of the disk untouched. (You’re going to want to click the translate link on the right side of the menu)

Selective File Wipe - Mac OS X

Permanent Eraser - Although Mac users have had the “secure empty trash” option, based on a multiple pass DoD method, since OS 10.3, Permanent Eraser offers peace of mind for those needing more assurance.

Selective File Wipe - Linux (Ubuntu)

Wipe Package from Ubuntu Unleashed - Adds secure multi-pass file deletion to your right click menu, like the aforementioned DeleteOnClick does in Windows.

The full article is worth the read and you can find it here:
http://lifehacker.com/5153684/properly-erase-your-physical-media