I've always liked BCWipe: http://www.jetico.com/bcwipepd.htm
But this isn't free; actually for the price of these things you are best to just purchase a new Hard drive. Unless you are doing multiple Hard drives
Either way, a guarantied wiped Hard drive is one that's been physically destroyed (imho)
This is a great post and makes me think of where I can fit in. I do a little bit of everything mentioned here and I guess I have to find my competitive advantage.