For HDDs: http://www.gaijin.at/en/dlwipedisk.php
SSDs typically came with a utility to do that.
For doing this complete erase to HDD, does it harm the drive?
For SSD, if Samsung, the Samsung SSD Magician?
And what about for Memory Cards/USB Pens?
Again for SSD and MemoryCards/USBPens, does it harm them when you write 0's or whatever on them?