I'm selling my laptop with a HD and I need some kind of software that will do a deep clean. I remember a bootdisk software that was being passed around a few years that did a deep clean that took around 24 hrs.
Eraser, which is based on DBAN but provides a GUI for it and some additional options. Just be careful with these tools and read everything onscreen - one mistake and you'll toast every drive in your box with a single click.
Low level formatting is a thing of the past, and technically should only be done one time in the lifetime of a hard drive, soooo... while there are actual low level formatting tools out there if you go digging around for 'em, they are not recommended and can actually damage a drive and render it useless if something goes wrong during the process.