This is an interesting topic. I have always had an interest in computer forensics and spent many hours a lot of forums. I have used many different software programs to test their performance. I have recovered all sorts of data from hard drives and removable media. There are a bunch of programs out there that claim they can recover data some work and many do not. The only way to truly eliminate data is to pulverize the hard drive to dust. There are 2 ways that data can be recovered through software and hardware. There are many algorithms that are used to wipe data all the way upto the Gutmann 35 passes. I knew a person that took a sledge hammer to shatter the drive and break the platters into many pieces. However these pieces were confiscated in case and using hardware techniques data was recovered. So drilling the platters or smashing the drive will not protect you. The bottomline where there is a will there is a way if someone is willing to spend money to get the data. Clean room data recovery is very expensive where the platters are reversed engineered. DBAN has been around for ages and works great it is a tired and trusted solution however please note there is NO guarantee your data cannot be recovered. You will not find any software that will put their neck on the line to say your data will NOT be recovered. That is a disclaimer to protect themselves from a lawsuit.
DBAN
When you get to FBI level of recovery they use a a very powerful program called Encase. It only costs about $3000.
Hope that helps.