In this wonderful age of identity theft, the experts have recommended destroying the hard drives of any computers you dispose of. In large cities, there are services that will shred the crap out of the thing for you for a fee.
In my case I dislike going into Denver and I'm cheap so I destroy HDD's in the following manner.
1. I disassemble the drive, which includes the circuit board that gets thrown in the trash after it's removed from the HDD chassis. You will need small Torx (T-9 and below) screwdrivers to get the HDD apart. I got a set of five Crapsman drivers from Sears for a reasonable price.
2. Once I get the drive open I rip out all the guts, which tends to wreck the read/write heads.
3. By this time the HDD platters are exposed to the filth of my shop and my fingerprints. I then place each platter in my vise that has knurled jaw faces and proceed to beat the $h!t out of each platter with a hammer turning it into a modern art origami potato chip shaped masterpiece.
I do keep the screws and platter spacers as they are cool.
Beware as Western Digital uses rare earth magnets in some/all of their HDD's and these suckers are strong as I found out the hard way.
After I got the WD HDD apart and destroyed, I was playing with the rare earth magnets attached to two head mounting brackets. One bracket had a needle like alignment pin attached to it. Yep, my thumb got between the magnets and the alignment pin went through my thumbnail. It hurt like bloody hell until I got the things separated and did a little first aid on my thumb. Surprisingly there wasn't much blood.