Software

If you are disposing of the drives, you can either use them for target practice or drill holes in them. 

If you want to recycle them you can create a PE boot disk that does a

diskpart:

select disk 0
clean
create partition primary
select partition 1
active
assign
exit

format:

format /p:1 /y /fs:ntfs c:

or you can use something below

http://pcsupport.about.com/od/toolsofthetrade/tp/free-data-destruction-software.htm

We have used Dukes Boot and Nuke. DBAN.