Below are some software that allows you to delete data from disks securely. All of them are pretty efficent and make it difficult for someone to recover the data. However keep in mind that no data is 100% unrecoverable to those who have sufficient time and money.
So it you have some really sensitive data that you have to destroy look into purchasing a furnace and melt the disks down and then destroy the remains.
Software for Data Wiping:
DBAN:
Darik’s Boot and Nuke (’DBAN’) is a self-contained boot floppy that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.
It’s a bootable floppy image that sterilizes IDE hard disks on x86 machines.
BCWipe software is designed to securely delete files from disks and other media
The utilities on this page allow you to destructively wipe/delete/erase a file, a disk (floppy disks, hard disks, etc), or a partition.
Active@ KillDisk is a powerful and compact DOS software that allows you to destroy all data on hard and floppy drives completely, excluding any possibility of future recovery of deleted files and folders.
Eraser is a powerful system security utility developed on the basis of advanced studies and research.